8-K

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the
Securities Exchange Act of 1934

Date of report (Date of earliest event reported): August 24, 2004

Aon CORPORATION

(Exact Name of Registrant as Specified in Charter)

Delaware	1-7933	36-3051915
(State or Other Jurisdiction of Incorporation)	(Commission File Number)	(IRS Employer Identification No.)
200 East Randolph Street, Chicago, Illinois		60601
(Address of Principal Executive Offices)		(Zip Code)

Registrant’s telephone number, including area code: (312) 381-1000

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

o            Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o            Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o            Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o            Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 5.04.Temporary Suspension of Trading Under Registrant’s Employee Benefit Plans.

On August 24, 2004, Aon Corporation (“Aon”) sent a notice to directors and executive officers of Aon informing them that a blackout period with respect to the Aon Savings Plan will be in effect beginning September 17, 2004 through October 7, 2004.  Aon provided the notice to its directors and executive officers in accordance with Section 306 of the Sarbanes-Oxley Act of 2002 and Rule 104 of Regulation BTR.  Aon received the notice required by Section 101(i)(12)(E) of the Employment Retirement Income Security Act of 1974, as amended, on August 18, 2004.

A copy of the notice is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

Item 9.01.Financial Statements and Exhibits.

(a)—(b)Not applicable.

(c)Exhibits:

Exhibit Number	Description of Exhibit
99.1	Notice of Blackout Period to Directors and Executive Officers of Aon Corporation dated August 24, 2004.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

	Aon CORPORATION
	By:	/s/ Patrick G. Ryan
		Patrick G. Ryan
		Chairman and Chief Executive Officer
Date: August 24, 2004

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EXHIBIT INDEX

Exhibit Number	Description of Exhibit
99.1	Notice of Blackout Period to Directors and Executive Officers of Aon Corporation dated August 24, 2004.

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EX-99.1

Exhibit 99.1

MEMORANDUM

TO:	All Directors and Executive Officers of Aon Corporation
FROM:	Jennifer L. Kraft
DATE:	August 24, 2004
SUBJECT:	Blackout Period with respect to Trading of Common Stock of Aon Corporation

The Aon Corporation (the “Company”) 401(k) Plan, known as the Aon Savings Plan (the “Savings Plan”), will be changing recordkeepers from AMVESCAP Retirement, Inc. to CitiStreet.  The conversion will require that a blackout period be imposed on participants’ transactions in the Savings Plan from September 17, 2004 through October 7, 2004 (the “Blackout Period”).  You will be informed if the timing of the Blackout Period changes.

Please be advised that the Blackout Period is scheduled to overlap with the Company’s regularly scheduled trading blackout period that commences on September 30, 2004 and which is scheduled to end two business days after the Company’s earnings for the third quarter are announced.  As a result, the regularly scheduled trading blackout period will extend beyond the Blackout Period.

1.You are not permitted to purchase, sell or otherwise acquire or transfer any equity securities of the Company (or derivative securities of those equity securities) during the Blackout Period.  Certain transactions are exempt from this prohibition, including, but not limited to, purchases or sales of Company securities pursuant to a Rule 10b5-1 arrangement (provided such arrangement is not adopted or amended during the Blackout Period).  There are also certain narrow exceptions for dividend reinvestment plans, certain automatic non-discretionary transactions within employee benefit plans (but not the Savings Plan), automatic formula grant programs, and exchanges by operation of law in connection with a merger or acquisition.

2.This prohibition is imposed because, during the Blackout Period, participants in the Savings Plan will not be permitted to enter into transactions under the Savings Plan with respect to Company securities because the Savings Plan will be changing recordkeepers from AMVESCAP Retirement, Inc. to CitiStreet.

3.The prohibition on sales and other transfers described in paragraph 1 above applies only to equity securities of the Company (and derivatives of such securities) that you have acquired in connection with your service or employment as a director or executive officer of the Company.  It is important to note that any such security you sell or otherwise transfer will be automatically treated as acquired in connection with your service or employment unless you establish that the securities were acquired from another source and this identification is consistent with your treatment of the securities for tax purposes and all other disclosure and reporting requirements.

4.Participants in the Savings Plan generally will be prohibited from engaging in certain transactions with respect to the Savings Plan beginning on September 17, 2004.  The Blackout Period is expected to last through October 7, 2004.  You will be informed if the timing of the Blackout Period changes.

5.For inquiries concerning either this Notice or the Blackout Period, please contact Jennifer L. Kraft, Associate General Counsel, Aon Corporation, 200 East Randolph Street, Chicago, Illinois 60601, (312) 381-5115, Jennifer_Kraft@aon.com.