SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                   FORM 10-Q/A

               X QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15 (d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

                FOR THE QUARTERLY PERIOD ENDED SEPTEMBER 30, 2001
                                       OR
                TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 (d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

                          COMMISSION FILE NUMBER 1-7933


                                 Aon CORPORATION
                                 ---------------
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

         DELAWARE                                          36-3051915
         --------                                          ----------
(STATE OR OTHER JURISDICTION OF                (IRS EMPLOYER IDENTIFICATION NO.)
INCORPORATION OR ORGANIZATION)

200 E. RANDOLPH ST. CHICAGO, ILLINOIS             60601
- -------------------------------------             -----
                                                 (ZIP CODE)
                (312) 381-1000
                --------------
       (REGISTRANT'S TELEPHONE NUMBER)


Indicate  by check  mark  whether  the  Registrant:  (1) has filed  all  reports
required to be filed by Section 13 or 15(d) of the  Securities  and Exchange Act
of 1934  during the  preceding  3 months (or for such  shorter  period  that the
Registrant was required to file such reports),  and (2) has been subject to such
filing requirements for the past 90 days. YES X  NO
                                             ---   ---

Number of shares of common stock outstanding:

       CLASS                                  NO. OUTSTANDING AS OF 9-30-01
       -----                                  -----------------------------

$1.00 par value Common                                269,217,702




         The  purpose of this Form  10-Q/A is to file an  amended  Exhibit 15 to
correct an error in the  Exhibit.  The date of the letter was  November 8, 2001,
and should have been November 13, 2001.

                                     PART II

                                OTHER INFORMATION


ITEM 6.         EXHIBITS AND REPORTS ON FORM 8-K

        (a)     Exhibits - The exhibits filed with this report are listed on the
                --------
                attached Exhibit Index.

        (b)     Reports on Form 8-K -
                -------------------

                (i)     No  Current  Reports  on Form  8-K  were  filed  for the
                        quarter ended  September 30, 2001.
                (ii)    The  Registrant  filed  one  Current  Report on Form 8-K
                        dated  November  8,  2001.  The  following  exhibit  was
                        included  in the  report:  Exhibit 99 -  Earnings  Press
                        Release issued on November 7, 2001.


SIGNATURE

Pursuant to the  Requirements  of the  Securities  and Exchange Act of 1934, the
Registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned thereunto duly authorized.

                                             Aon CORPORATION
                                             ---------------
                                             (Registrant)



November 28, 2001                            /s/ Harvey N. Medvin
                                             --------------------
                                             HARVEY N. MEDVIN
                                             EXECUTIVE VICE PRESIDENT
                                              AND CHIEF FINANCIAL OFFICER
                                             (Principal Financial and Accounting
                                             Officer)

                                     - 2 -

Aon CORPORATION
- ---------------

Exhibit Number In Regulation S-K

Item 601 Exhibit Table
- ----------------------

* (12) Statements regarding Computation of Ratios.

                (a)     Statement regarding  Computation of Ratio of Earnings to
                        Fixed Charges.

                (b)     Statement regarding  Computation of Ratio of Earnings to
                        Combined Fixed Charges and Preferred Stock Dividends.


  (15) Letter re: Unaudited Interim Financial Information

__________
*Previously filed.

                                     - 3 -

                                                                      Exhibit 15


Board of Directors and Stockholders
Aon Corporation


We are aware of the incorporation by reference in the Registration Statements of
Aon  Corporation  ("Aon")  described in the following  table of our report dated
November  13, 2001  relating to the  unaudited  condensed  consolidated  interim
financial  statements of Aon Corporation  that are included in its Form 10-Q for
the quarter ended September 30, 2001:

         Registration Statement
         ----------------------
         Form            Number                  Purpose
         ----            ------                  -------

         S-8          33-27984         Pertaining to Aon's savings plan
         S-8          33-42575         Pertaining to Aon's stock award plan and
                                          stock option plan
         S-8          33-59037         Pertaining to Aon's stock award plan and
                                          stock option plan
         S-4          333-21237        Offer to exchange Capital Securities of
                                          Aon Capital A
         S-3          333-50607        Pertaining to the registration of 369,000
                                          shares of common stock
         S-8          333-55773        Pertaining  to Aon's  stock  award plan,
                                          stock  option  plan and employee stock
                                          purchase plan
         S-3          333-78723        Pertaining to the registration  of debt
                                          securities, preferred stock and common
                                          stock
         S-3          333-49300        Pertaining to the registration of
                                          3,864,824 shares of common stock
         S-4          333-57706        Pertaining to the registration of up to
                                          3,852,184 shares of common stock
         S-3          333-65624        Pertaining to the registration of
                                          2,000,000 shares of common stock

Pursuant to Rule 436(c) of the  Securities Act of 1933, our report is not a part
of the registration  statements  prepared or certified by accountants within the
meaning of Section 7 or 11 of the Securities Act of 1933.


                                                        ERNST & YOUNG LLP



Chicago, Illinois
November 13, 2001