June 28, 2005





Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C.   20549

         RE:      REPORT ON FORM 11-K FOR THE AON SAVINGS PLAN
                  REGISTRANT:  AON CORPORATION
                  COMMISSION FILE NO.:  1-7933


Gentlemen and Ladies:

         Enclosed with this EDGAR transmission is the above referenced Form 11-K
for the Aon Savings Plan.

         Please  contact  the  undersigned  at  312/381-3165  if  you  have  any
questions.

Very truly yours,


/S/ BETH E. BURK

Beth E. Burk
Associate General Counsel - Benefits

BEB/rjr
Enclosures



                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                    FORM 11-K





__X__    Annual Report Pursuant to Section 15(d) of the Securities
                  Exchange Act of 1934

                  For the fiscal year ended December 31, 2004

                                       OR

_____             Transition Report Pursuant to Section 15(d) of the
                  Securities Exchange Act of 1934



                  A.       Full  title of the plan and the  address of the plan,
                           if different from the issuer named below:

                                Aon Savings Plan


                  B.       Name of the issuer of the securities held pursuant to
                           the plan and the address of its  principal  executive
                           office:


                                 Aon Corporation
                              200 E. Randolph Drive
                             Chicago, Illinois 60601








                               S I G N A T U R E S

Pursuant to the  requirements of the Securities  Exchange Act of 1934, the Plan,
by the Plan  Administrator,  the Committee,  has caused this annual report to be
signed on its  behalf by the  undersigned,  thereunto  duly  authorized,  in the
County of Cook and the State of Illinois on the 28th day of June, 2005.

AON SAVINGS PLAN

BY THE COMMITTEE



/s/ THOMAS STACHURA                         /s/ JOHN A. RESCHKE               
-------------------                         -------------------
Thomas Stachura                             John A. Reschke




                 FINANCIAL STATEMENTS AND SUPPLEMENTAL SCHEDULE

                                AON SAVINGS PLAN

                     Years Ended December 31, 2004 and 2003

                      With Report of Independent Registered

                             Public Accounting Firm

                    Employer Identification Number 36-3051915

                                   Plan # 020






                                AON SAVINGS PLAN

                 FINANCIAL STATEMENTS AND SUPPLEMENTAL SCHEDULE

                     Years ended December 31, 2004 and 2003


                                    CONTENTS



Report of Independent Registered Public Accounting Firm                        1

Financial Statements

         Statement of Assets Available for Benefits
         at December 31, 2004 and 2003                                         2

         Statement of Changes in Assets Available for Benefits
         for the years ended December 31, 2004 and 2003                        3

Notes to Financial Statements                                                  4

Supplemental Schedule:

         Schedule H, Line 4i - Schedule of Assets (Held At
         End of Year)                                                         12




             Report of Independent Registered Public Accounting Firm


The Participants and Administrative Committee
Aon Savings Plan


We have audited the accompanying  statements of assets available for benefits of
the Aon  Savings  Plan  as of  December  31,  2004  and  2003,  and the  related
statements of changes in assets available for benefits for the years then ended.
These financial statements are the responsibility of the Plan's management.  Our
responsibility  is to express an opinion on these financial  statements based on
our audits.

We conducted our audits in accordance  with the standards of the Public  Company
Accounting Oversight Board (United States). Those standards require that we plan
and perform the audit to obtain reasonable assurance about whether the financial
statements are free of material misstatement.  We were not engaged to perform an
audit of the  Plan's  internal  control  over  financial  reporting.  Our audits
included  consideration of internal control over financial  reporting as a basis
for designing audit  procedures that are appropriate in the  circumstances,  but
not for the purpose of expressing an opinion on the  effectiveness of the Plan's
internal  control  over  financial  reporting.  Accordingly,  we express no such
opinion. An audit also includes examining,  on a test basis, evidence supporting
the  amounts  and  disclosures  in  the  financial  statements,   assessing  the
accounting  principles  used and significant  estimates made by management,  and
evaluating the overall  financial  statement  presentation.  We believe that our
audits provide a reasonable basis for our opinion.

In our opinion,  the financial  statements  referred to above present fairly, in
all material respects, the assets available for benefits of the Plan at December
31, 2004 and 2003, and the changes in its assets  available for benefits for the
years  then  ended,  in  conformity  with  U.S.  generally  accepted  accounting
principles.

Our audits  were  performed  for the  purpose of forming an opinion on the basic
financial statements taken as a whole. The accompanying supplemental schedule of
assets (held at end of year) as of December 31, 2004,  is presented for purposes
of additional  analysis and is not a required part of the financial  statements,
but is supplementary information required by the Department of Labor's Rules and
Regulations for Reporting and Disclosure  under the Employee  Retirement  Income
Security Act of 1974. This  supplemental  schedule is the  responsibility of the
Plan's management.  The supplemental schedule has been subjected to the auditing
procedures  applied in our audits of the basic financial  statements and, in our
opinion,  is fairly  stated in all  material  respects  in relation to the basic
financial statements taken as a whole.


Chicago, Illinois                                             Ernst & Young LLP
June 6, 2005

                                        1




                                                                            Employer Plan Identification # 36-3051915
                                                                            Plan # 020



                                                          AON SAVINGS PLAN
                                             STATEMENT OF ASSETS AVAILABLE FOR BENEFITS

                                                           (in thousands)


                                                                                                   DECEMBER 31
                                                                          ----------------------------------------------------------

                                                                                  2004                              2003
                                                                          -----------------------            -----------------------
                                                                                                                          

     ASSETS:
     ------

     Investments, at Fair Value:
          Aon Corporation Common Stock                                $                  258,761         $                  302,540
          Brokerage Accounts-Other Common and
             Preferred Stocks and Mutual Funds                                             9,215                              8,327
          Investments held in Mutual Funds:
             State Street Global Advisors Short Term Investment Fund                     254,613                                  -
             AIM Liquid Asset Fund                                                             -                            249,360
             Vanguard REIT Index Fund                                                     74,396                             53,303
             Vanguard Admiral Intermediate Term Treasury Fund                             73,341                             76,522
             Vanguard Capital Opportunities Fund                                          60,849                                  -
             INVESCO Dynamics Fund                                                             -                             31,136
             Dodge & Cox Common Stock Fund                                               174,806                            105,230
             PIMCO Total Return Fund                                                      49,788                             40,609
             Montag & Caldwell Growth Fund                                                23,285                             15,855
             Managers Special Equity Fund                                                 53,183                             35,821
             Templeton Emerging Markets Fund                                                   -                             16,645
             American Funds Euro-Pacific Growth Fund                                      77,495                                  -
          Investments held in Collective Trusts:
             Ned Davis Research Asset Allocation Strategy Fund                           138,855                                  -
             State Street Global Advisors S&P 500 Strategy Fund                          255,803                                  -
             INVESCO Asset Allocation Fund                                                     -                            136,138
             INVESCO 500 Index Fund                                                            -                            229,043
             INVESCO International Equity Fund                                                 -                             40,756
          Short-Term Investment Funds                                                      1,943                              2,065
     Participant Loans                                                                    23,335                             21,239
                                                                          -------------------------          -----------------------

                                                                                       1,529,668                          1,364,589

     CONTRIBUTIONS RECEIVABLE:
     Participant Contribution Receivable                                                   2,517                                  -
     Company Contribution Receivable                                                       9,219                             54,148
                                                                          -----------------------            -----------------------

                                                                                          11,736                             54,148


                                                                          -------------------------          -----------------------
     ASSETS AVAILABLE FOR BENEFITS                                    $                1,541,404         $                1,418,737
                                                                          =========================          =======================



          See notes to financial statements.


                                        2




                                                                            Employer Plan Identification # 36-3051915
                                                                            Plan # 020




                                                          AON SAVINGS PLAN
                                        STATEMENT OF CHANGES IN ASSETS AVAILABLE FOR BENEFITS

                                                           (in thousands)

                                                                                                    DECEMBER 31
                                                                          ----------------------------------------------------------

                                                                                  2004                              2003
                                                                          -----------------------            -----------------------

                                                                                                                          
     NET INVESTMENT INCOME
          Interest Income                                             $                    3,574         $                    1,355
          Net Appreciation in Fair Value
             of Investments                                                               89,855                            201,742
          Aon Corporation Dividends                                                        7,145                              7,948
          Other Dividends                                                                 21,339                             14,705
          Management and Administrative Fees                                              (1,580)                            (3,076)
                                                                          -----------------------            -----------------------

     TOTAL NET INVESTMENT INCOME                                                         120,333                            222,674

     CONTRIBUTIONS
          Company                                                                         42,707                             54,148
          Participants                                                                    98,380                             90,764
          Rollovers                                                                        5,573                              7,580
                                                                          -----------------------            -----------------------

     TOTAL CONTRIBUTIONS                                                                 146,660                            152,492

     OTHER CHANGES

          Benefit Payments                                                              (144,326)                           (98,081)
          Plan Mergers                                                                         -                              6,144
                                                                          -----------------------            -----------------------

     TOTAL OTHER CHANGES                                                                (144,326)                           (91,937)
                                                                          -----------------------            -----------------------

     NET INCREASE IN ASSETS AVAILABLE
         FOR BENEFITS                                                                    122,667                            283,229

     ASSETS AVAILABLE FOR BENEFITS
         AT BEGINNING OF YEAR                                                          1,418,737                          1,135,508
                                                                          -----------------------            -----------------------

     ASSETS AVAILABLE FOR BENEFITS
         AT END OF YEAR                                               $                1,541,404         $                1,418,737
                                                                          =======================            =======================



          See notes to financial statements.


                                        3



                                       Employer Plan Identification # 36-3051915
                                       Plan # 020


                                AON SAVINGS PLAN

                          NOTES TO FINANCIAL STATEMENTS

                     Years Ended December 31, 2004 and 2003

1.       DESCRIPTION OF PLAN

         GENERAL

         The Aon  Savings  Plan  (the  Plan)  was  authorized  by the  Board  of
         Directors of Aon  Corporation  (the Company or Plan  Sponsor).  It is a
         defined  contribution  plan  with  a  salary  deferral  feature  and an
         employee stock  ownership  (ESOP)  feature.  The Plan is subject to the
         provisions  of the  Employee  Retirement  Income  Security  Act of 1974
         (ERISA).  Effective  January 1, 2003,  the ASI Solutions,  Inc.  401(k)
         Retirement  Plan and the McLagan  Partners Inc.  401(k) Profit  Sharing
         Plan were  merged into the Plan and as a result,  assets  approximating
         $6.1 million were transferred to the Plan.  Effective  January 1, 2004,
         the Aon Retirement  Account was established as a separate account under
         the Aon  Savings  Plan.  The Aon  Retirement  Account is  intended  for
         employees  hired  after  January  1,  2004  who  are not  eligible  for
         participation in the Aon Pension Plan.

         The assets of the ESOP  portion of the Plan are  invested  primarily in
         common stock of the Company. Additionally,  certain assets are invested
         by the  Trustees as deemed  advisable in order for the Plan to meet its
         cash flow needs.

         Effective  January  1,  2003,  the Aon  Common  Stock Fund and the ESOP
         Allocated  Fund were  merged  into a single  fund called the Aon Common
         Stock ESOP Fund.  Participants have the option to reinvest dividends in
         additional  shares of Aon common stock in the Plan or receive dividends
         in cash.  Additionally,  effective  January 1, 2003,  participants  are
         allowed to  immediately  diversify any Company  matching  contributions
         allocated to the Aon Common Stock ESOP Fund.

         The   following   description   of  the  Plan   provides  only  general
         information.  Participants of the Plan should refer to the Summary Plan
         Description for a more complete description of the Plan.

         ELIGIBILITY AND PARTICIPATION

         Employees other than field sales agents or employees  scheduled to work
         less than 20 hours per week are  immediately  eligible to  participate.
         Field sales agents and  employees  scheduled to work less than 20 hours
         per week are  eligible  to  participate  after  completing  one year of
         service.  Participants must complete one year of service to be eligible
         for Company matching contributions.


                                        4


1.       DESCRIPTION OF PLAN (CONTINUED)

         CONTRIBUTIONS

         PARTICIPANT  - Participant  contributions  are made by means of regular
         payroll deductions.  Non-highly compensated participants, as defined by
         the  Internal  Revenue  Code  (IRC),  may  elect to make  contributions
         between   1%  and  25%  (16%   prior  to  January  1,  2004)  of  their
         compensation,  as defined by the Plan. Highly compensated participants,
         as defined by the IRC, may elect to make  contributions  between 1% and
         10% (8% prior to January 1, 2004) of their compensation,  as defined by
         the Plan.  Participant  contributions are limited to amounts allowed by
         the  Internal   Revenue   Service  (IRS).   Accordingly,   the  maximum
         participant  contribution  was $13,000 in 2004 and $12,000 in 2003.  In
         addition to regular participant  contributions,  catch-up contributions
         of up to  $3,000  for 2004 and  $2,000  for 2003 were  allowed  for any
         participants who were age 50 or older during the Plan year.

         The Aon Retirement Account is funded entirely by Company contributions.
         No employee contributions are allowed.

         COMPANY - For 2004,  the Company  contributes an amount equal to 50% of
         the  first  6%  of a  participant's  compensation  that  a  participant
         contributes to the Plan (75% of a  participant's  compensation up to 4%
         for employees of Aon Human Capital Services,  LLC and 100% of the first
         3%  for  employees  of  Human  Resources   Outsourcing   Group).   This
         contribution  will be made concurrent with  participant  contributions.
         Employees of the Human  Resources  Outsourcing  Group receive a further
         contribution equal to 75% of the next 3% of compensation contributed to
         the Plan.  The  Company may make a further  discretionary  contribution
         based on employee  contributions of up to 6%. The amount and allocation
         of this contribution is determined by the Aon Board of Directors.

         For 2003, the Company  contributed an amount equal to 100% of the first
         3% of a participant's  compensation  that a participant  contributed to
         the Plan (75% of a participant's compensation up to 4% for employees of
         Aon  Human  Capital   Services,   LLC).  The  Company  made  a  further
         contribution  to the ESOP  portion  of the  Plan  equal to 75% (50% for
         field sales agents) of the next 3% of a participant's compensation that
         is contributed to the Plan. In 2003, the ESOP  contribution was made in
         cash. Employees of Aon Human Capital Services, LLC are not eligible for
         the ESOP contribution. The Plan requires that a participant be employed
         for at least one year and be  actively  employed  as of the last day of
         the Plan year in order to receive a Company contribution.

         INVESTMENT OPTIONS

         Contributions  to the  Plan  may  be  invested  in  any of the  various
         investment  alternatives  offered by the Plan in any whole percentages.
         Additionally,  a Self-Managed  Account is offered whereby  participants
         can invest their  self-directed  contributions in various stock, mutual
         funds and other investments.
 

                                        5


1.       DESCRIPTION OF PLAN (CONTINUED)

         PARTICIPANT ACCOUNTS

         Each   participant's   account  is  credited  with  the   participant's
         contribution and allocations of a) the Company's  contributions  and b)
         Plan earnings (losses).  The benefit to which a participant is entitled
         is the benefit that can be provided from the participant's account.

         VESTING

         For the ESOP portion of the Plan, a participant vests in 20% increments
         per year and becomes 100% vested after completion of five years of plan
         service.

         For the non-ESOP portion of the Plan,  participants are fully vested in
         their  contributions plus actual earnings thereon.  Participants become
         100% vested in the remainder of their account  balance after five years
         of plan service, according to a graded schedule.

         Participants  will become  fully vested in the Aon  Retirement  Account
         after five years of service.

         The  total  amount  of  forfeitures   allocated  to  participants   was
         $1,074,000 for 2003. For 2004,  $1,538,000 of forfeitures  were used to
         provide  partial  funding  for Company  contributions  and to pay other
         expenses of the Plan.

         BENEFIT PAYMENTS

         For the ESOP portion of the Plan, a participant's  entire account shall
         be paid to the participant or designated beneficiary in a lump sum upon
         normal retirement,  permanent  disability or death. The participant may
         elect payment in the form of Company common stock or cash.

         For the non-ESOP  portion,  on  termination  of service,  a participant
         shall  be paid a lump  sum  amount  equal  to the  value  of his or her
         account. The participant will receive payment in the form of cash only.

         PLAN TERMINATION

         Although it has not  expressed any intent to do so, the Company has the
         right under the Plan to discontinue its  contributions  at any time and
         to terminate the Plan subject to the provisions of ERISA.  In the event
         of Plan  termination,  participants  will  become  100% vested in their
         accounts.


                                        6


1.       DESCRIPTION OF PLAN (CONTINUED)

         PARTICIPANT LOANS

         Under the loan provision of the Plan, each participant is permitted one
         loan in a twelve month period and the outstanding  balance of all loans
         made to a  participant  may not  exceed the lesser of $50,000 or 50% of
         the vested  portion of the  participant's  account,  excluding the ESOP
         portion of the account.  The interest rate for each loan is equal to 1%
         plus the prime rate as quoted in The Wall  Street  Journal for the last
         day of the  month  preceding  the loan  request.  Loans  are made for a
         period of up to five years,  except for  residential  loans that have a
         fixed repayment period of up to fifteen years.

2.       SIGNIFICANT ACCOUNTING POLICIES

         BASIS OF ACCOUNTING

         The  financial  statements of the Plan are prepared on an accrual basis
         in accordance with U.S. generally accepted accounting principles.

         INVESTMENT VALUATION AND INCOME RECOGNITION

         Investments are carried at fair value, which for marketable  securities
         is based on quotations obtained from national securities  exchanges and
         various  other   sources.   Participant   loans  are  valued  at  their
         outstanding balances, which approximate fair value.

         Interest  income is recorded as earned.  Dividend income is recorded on
         the ex-dividend  date.  Realized gains or losses on investments are the
         difference  between the proceeds  received and the cost of  investments
         sold as determined on a first-in,  first-out  basis.  The change in the
         difference  between fair value and the cost of  investments is reported
         as unrealized appreciation or depreciation of investments.

         ADMINISTRATIVE EXPENSES

         Administrative   expenses  of  the  Plan,  including  expenses  of  the
         Trustees,  are paid from the Plan assets, except to the extent that the
         Company,  at its  discretion,  may  decide  to pay such  expenses.  The
         Company did not pay any Plan expenses in 2004 or 2003.

         USE OF ESTIMATES

         The  preparation  of the financial  statements in conformity  with U.S.
         generally accepted  accounting  principles  requires management to make
         estimates  and  assumptions  that  affect the  amounts  reported in the
         financial  statements  and  accompanying  notes.  Actual  results could
         differ from those estimates.


                                        7


3.       INVESTMENTS

         Effective  October 1, 2004,  State  Street Bank and Trust  Comapnay has
         been appointed Trustee and custodian for all Plan assets. Prior to this
         date,  Institutional  Trust  Company  (ITC) was  custodian  of the Plan
         assets and Trustee for all Plan assets except the Aon Common Stock ESOP
         shares  and the  self-managed  brokerage  accounts.  For the Aon Common
         Stock ESOP shares and  self-managed  brokerage  accounts,  State Street
         Bank  and  Trust  Company  was the  Trustee.  The  Trustees  are  named
         fiduciaries  under  ERISA.  As used herein,  Trustee  refers to ITC and
         State Street Bank and Trust Company individually and collectively.


                                        8


3.       INVESTMENTS (CONTINUED)

         During  2004 and 2003 the  Plan's  investments  (including  investments
         bought,  sold and held during the year)  appreciated  (depreciated)  in
         fair value as follows (in thousands):



                                                                                       December 31
                                                                          2004                              2003
                                                   --------------------------------------------------------------------
                                                                     Net Realized                        Net Realized
                                                                   and Unrealized                      and Unrealized
                                                                     Appreciation                        Appreciation
                                                                   (Depreciation)                      (Depreciation)
                                                                    in Fair Value                       in Fair Value
                                                                   of Investments                      of Investments
                                                          Fair             During             Fair             During
                                                          Value          the Year             Value          the Year
                                                   --------------------------------------------------------------------
                                                                                                       
Investments, at fair value:
Aon Corporation Common Stock                       $       258,761 $           606 $         302,540 $          65,964
Brokerage Accounts-Other
  Common and Preferred Stocks
  and Mutual Funds                                           9,215            (38)             8,327             2,337
Investments in Mutual Funds:
  State Street Global Advisors Short
     Term Investment Fund                                  254,613               -                 -                 -
  AIM Liquid Asset Fund                                          -               -           249,360                 -
  Vanguard REIT Index Fund                                  74,396          13,335            53,303            10,518
  Vanguard Capital Opportunities Fund                       60,849           6,851                 -                 -
  INVESCO Dynamics Fund                                          -             803            31,136             7,901
  Dodge & Cox Common Stock Fund                            174,806          19,224           105,230            19,582
  PIMCO Total Return Fund                                   49,788           (199)            40,609                37
  Montag & Caldwell Growth Fund                             23,285             785            15,855             1,894
  Managers Special Equity Fund                              53,183           6,521            35,821             8,334
  Templeton Emerging Markets
      Fund                                                       -            (55)            16,645             3,267
  American Euro-Pacific Growth Fund                         77,495           9,692                 -                 -
  Vanguard Admiral Intermediate
      Term Treasury Fund                                    73,341         (1,009)            76,522           (3,003)
Investments in Collective Trusts:
  State Street Asset Allocation Fund                             -         (1,901)                 -                 -
  Ned Davis Research Asset
      Allocation Fund                                      138,855           7,739                 -                 -
  State Street Global Advisors S&P 500
      Strategy Fund                                        255,803          21,150                 -                 -
  INVESCO Asset Allocation Fund                                  -           1,653           136,138            23,219
  INVESCO 500 Index Fund                                         -           4,220           229,043            51,876
  INVESCO International
        Equity Fund                                              -             478            40,756             9,816
Short-Term Investment Funds                                  1,943               -             2,065                 -
                                                   --------------------------------------------------------------------
  Total                                            $     1,506,333 $        89,855 $       1,343,350 $         201,742
                                                   --------------------------------------------------------------------




                                        9


3.       INVESTMENTS (CONTINUED)

         The fair value of individual  investments  that represent 5% or more of
         the Plan's assets is as follows (in thousands):



                                                                           December 31
                                                             -------------------------------------

                                                                   2004                    2003
                                                                   ----                    ----
                                                                                        
         Aon Corporation, Common Stock                        $   258,761              $  302,540
         Investments in Mutual Funds:
           State Street Global Advisors Short
              Term Investment Fund                                254,613                       -
           AIM Liquid Asset Fund                                        -                 249,360
           Dodge & Cox Common Stock Fund                          174,806                 105,230
           Vanguard Admiral Intermediate Term
              Treasury Fund                                             *                  76,522
           American Euro-Pacific Growth Fund                       77,495                       -
         Investments in Collective Trusts:
           Ned Davis Research Asset Allocation
               Strategy Fund                                      138,855                       -
           State Street Global Advisors S&P 500
               Strategy Fund                                      255,803                       -
           INVESCO 500 Index Fund                                       -                 229,043
           INVESCO Asset Allocation Fund                                -                 136,138

         *Below 5% threshold.




4.       INCOME TAX STATUS

         The Plan has received a determination letter from the IRS dated October
         1, 2003, stating that the Plan is qualified under section 401(a) of the
         IRC  and,  therefore,  the  related  trust  is  exempt  from  taxation.
         Subsequent to this issuance of the determination  letter,  the Plan was
         amended. Once qualified,  the Plan is required to operate in conformity
         with the IRC to maintain  its  qualification.  The Plan  Administrative
         Committee  believes the Plan is being  operated in compliance  with the
         applicable  requirements of the IRC and,  therefore,  believes that the
         Plan, as amended, is qualified and the related trust is tax exempt.

5.       RISKS AND UNCERTAINTIES

         The  Plan  invests  in  various   investment   securities.   Investment
         securities are exposed to various risks such as interest  rate,  market
         and credit  risks.  Due to the level of risk  associated  with  certain
         investment securities,  it is at least reasonably possible that changes
         in the values of investment  securities will occur in the near term and
         that  such  changes  could  materially  affect  participants'   account
         balances and the amounts reported in the statements of assets available
         for benefits.


                                       10


6.       SUBSEQUENT EVENTS

         Effective in 2005,  distributions  to  participants  whose balances are
         between  $1,000 and $5,000 and that are made without their consent must
         be rolled over into an IRA account.


                                       11



                                                                                Employer Identification #  36-3051915
                                                                                Plan #  020
                                                   AON SAVINGS PLAN
                            Schedule H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)
                                                   December 31, 2004

                                                             Number of Shares                       Current Value
Identity of Issuer                                           Principal Amount                        (thousands)
------------------------------------------------------------------------------------------------------------------
                                                                                                        
AON COMMON STOCK ESOP FUND
--------------------------

COMMON STOCK

     Aon Corporation
     Common Stock, 1.00 par*                                  10,884,365                         $        258,679
                                                                                                    ==============


SHORT TERM INVESTMENT FUND
--------------------------

MUTUAL FUND

     Investments held in the State Street Global
     Advisor Short Term Investment Fund*                     254,613,324                         $        254,613
                                                                                                    ==============


TOTAL RETURN FUND
-----------------

COLLECTIVE TRUST

     Investments held in the Ned Davis Research
     Asset Allocation Fund                                    11,161,666                         $        138,855
                                                                                                    ==============


COMMON STOCK INDEX FUND
-----------------------

COLLECTIVE TRUST

     Investments held in the State Street Global
     Advisors S&P 500 Strategy Fund*                           1,156,515                         $        255,803
                                                                                                    ==============


REAL ESTATE SECURITIES FUND
---------------------------

MUTUAL FUND

     Investments held in the Vanguard
     REIT Index Fund                                           5,999,641                         $         74,396
                                                                                                    ==============



                                       12



                                                                                Employer Identification #  36-3051915
                                                                                Plan #  020
                                                   AON SAVINGS PLAN
                            Schedule H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)
                                                   December 31, 2004
                                                      (continued)

                                                             Number of Shares                       Current Value
Identity of Issuer                                           Principal Amount                        (thousands)
------------------------------------------------------------------------------------------------------------------
                                                                                                        
VANGUARD CAPITAL OPPORTUNITIES FUND
-----------------------------------

MUTUAL FUND

     Investments held in the Vanguard Capital
     Opportunities Fund                                          856,070                         $         60,849
                                                                                                    ==============


DODGE & COX COMMON STOCK FUND
-----------------------------

MUTUAL FUND

     Investments held in the Dodge & Cox
     Common Stock Fund                                         1,342,387                         $        174,806
                                                                                                    ==============


PIMCO TOTAL RETURN FUND
-----------------------

MUTUAL FUND

     Investments held in the PIMCO
     Total Return Fund                                         4,666,161                         $         49,788
                                                                                                    ==============


MONTAG & CALDWELL GROWTH FUND
-----------------------------

MUTUAL FUND

     Investments held in the Montag & Caldwell
     Growth Fund                                               1,024,883                         $         23,285
                                                                                                    ==============


MANAGERS SPECIAL EQUITY FUND
----------------------------

MUTUAL FUND

     Investments held in the Managers
     Special Equity Fund                                         588,244                         $         53,183
                                                                                                    ==============



                                       13




                                                                                Employer Identification #  36-3051915
                                                                                Plan #  020
                                                   AON SAVINGS PLAN
                            Schedule H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)
                                                   December 31, 2004
                                                      (continued)

                                                             Number of Shares                       Current Value
Identity of Issuer                                           Principal Amount                        (thousands)
------------------------------------------------------------------------------------------------------------------
                                                                                                        
VANGUARD ADMIRAL INTERMEDIATE TERM
----------------------------------
    TREASURY FUND
    -------------

MUTUAL FUND
-----------

     Investments held in the Vanguard Admiral
     Intermediate Term Treasury Fund                           6,513,415                         $         73,341
                                                                                                    ==============

AMERICAN EURO-PACIFIC GROWTH FUND
---------------------------------

MUTUAL FUND

     Investments held in the American Euro-
     Pacific Growth Fund                                       2,175,591                         $         77,495
                                                                                                    ==============

OTHER COMMON AND PREFERRED STOCKS AND MUTUAL FUNDS (SELF-MANAGED FUNDS)
-----------------------------------------------------------------------

BROKERAGE ACCOUNTS

     Investments held in other common and preferred
     stocks and mutual funds and other investments             9,214,966                         $          9,215
                                                                                                    ==============

    Investments held in Aon Corporation
    Common Stock*                                              3,426                             $             82
                                                                                                    ==============

    Investment held in the State Street
    Short-Term Investment Fund*                                1,943,410                         $          1,943
                                                                                                    ==============


PARTICIPANT LOANS (5.00% - 11.0%)                                      -                         $         23,335
                                                                                                    ==============

                                                                                                 $      1,529,668
                                                                                                    ==============

    *Party in interest transaction not prohibited by ERISA.





                                       14


            CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM


We consent to the incorporation by reference in the Registration Statement (Form
S-8 No.  33-27894)  pertaining to the Aon Savings Plan of Aon Corporation of our
report dated June 6, 2005, with respect to the financial statements and schedule
of the Aon Savings Plan  included in this annual report (Form 11-K) for the year
ended December 31, 2004.





Chicago, Illinois                                             Ernst & Young LLP
June 27, 2005