SC TO-C

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE TO

(RULE 13e-4)

TENDER OFFER STATEMENT

UNDER SECTION 14(d)(1) OR 13(e)(1) OF THE SECURITIES EXCHANGE ACT OF 1934

Aon Corporation

(Name of Subject Company (Issuer) and Filing Person (Offeror))

Options to Purchase Common Stock, $1.00 Par Value Per Share

(Title of Class of Securities)

037389103

(CUSIP Number of Class of Securities)

(Underlying Common Stock)

D. Cameron Findlay

Executive Vice President and General Counsel

Aon Corporation

200 East Randolph Street

Chicago, IL 60601

(312) 381-1000

(Name, address and telephone number of person authorized to receive notices and communications on behalf of filing person)

With a Copy to:

Terrence R. Brady

Winston & Strawn LLP

35 W. Wacker Drive

Chicago, IL 60601

(312) 558-5600

CALCULATION OF FILING FEE

Transaction valuation	Amount of filing fee
Not Applicable*	Not Applicable
*  No filing fee is required because this filing contains only preliminary communications made before the commencement of
a tender offer.

o Check box if any part of the fee is offset as provided by Rule 0-11(a)(2) and identify the filing with which the offsetting fee was previously paid. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.

Amount Previously Paid:	Not applicable.	Filing party:	Not applicable.
Form or Registration No.:	Not applicable.	Date filed:	Not applicable.

x Check the box if the filing relates solely to preliminary communications made before the commencement of a tender offer.

Check the appropriate boxes below to designate any transactions to which the statement relates:

o third party tender offer subject to Rule 14d-1.

x issuer tender offer subject to Rule 13e-4.

o going-private transaction subject to Rule 13e-3.

o amendment to Schedule 13D under Rule 13d-2.

Check the following box if the filing is a final amendment reporting the results of the tender offer:o

This Tender Offer Statement on Schedule TO is being filed by Aon Corporation, a Delaware corporation, pursuant to General Instruction D to Schedule TO.

ITEM 12.   EXHIBITS.

(a)(1)(b)      Email to Eligible Option Holders from Danita E Dallman, dated August 10, 2007.

2

EXHIBIT INDEX

Exhibit Number	Description
(a)(1)(b)	Email to Eligible Option Holders from Danita E Dallman, dated August 10, 2007.

3

EX-99.(A)(1)(B)

Exhibit (a)(1)(b)

Email to Eligible Option Holders from Danita E Dallman, dated August 10, 2007

Subject:  Important Information Concerning Your Aon Stock Options

FROM THE EXECUTIVE COMPENSATION DEPARTMENT

As you may be aware, we recently concluded a voluntary review of Aon’s stock option granting practices.  We determined that Aon’s procedures relating to certain stock option grants caused incorrect measurement dates to be used for financial accounting and tax purposes.

You are receiving this e-mail because we have determined that, as a result of this review, one or more of your stock option awards was granted at a “discounted” exercise price (i.e., when the exercise price is less than the fair market value of the stock on the deemed date of grant).  As a result, the affected stock options could subject you to adverse personal tax consequences unless those stock options are corrected as explained below.

We will be offering you an opportunity to participate in a special stock option amendment program with respect to your unexercised affected stock options.  The stock option amendment program will be conducted by means of a tender offer.  Under the program you will be able to elect to amend your stock option grant to “cure” it from adverse tax treatment based on the discount recognized for accounting purposes.

We anticipate that the tender offer program will be available beginning on August 15, 2007. You will receive formal notice of the program, and your eligibility to participate in it, at that time.  Also included in the information will be communication regarding a recorded web-based telecast, that will help explain the potentially adverse tax impact of the discounted options and how we are offering to address the situation and the choices you will need to make.  Finally, we will also communicate with you about your affected stock options so you know exactly which stock options are at issue and provide you with dedicated contact resources who could answer your questions.

Please note that you are free to exercise your stock options at any time.  However, if you do not elect to participate in the tender offer program once it becomes available and you instead choose to exercise affected stock options, you will be responsible for potential incremental taxes and penalties.   We do not intend for you to bear the burden of such adverse tax consequences.  Accordingly, we hope that you elect to participate in the tender offer program when it becomes available.

Thanks in advance for your patience as we work to correct this matter.

(a)(1)(b)-1