Mail Stop 05-07
        April 28, 2005

Via U.S. Mail
Aon Corporation
Patrick Ryan, Chairman
200 E. Randolph Street
Chicago, IL 60601

RE:		Aon Corporation
      Form 10-K for the fiscal year ended December 31, 2004
		File No. 1-07933

Dear Mr. Ryan:

      We have limited our review of your Form 10-K to disclosures
relating to your contacts with countries that have been identified
as
state sponsors of terrorism, and will make no further review of
the
Form 10-K.  Our review with respect to this issue does not
preclude
further review by the Assistant Director group with respect to
other
issues.  At this juncture, we are asking you to provide us with
supplemental information, so that we may better understand your
disclosure.  Please be as detailed as necessary in your response.
After reviewing this information, we may or may not raise
additional
comments.

      Please understand that the purpose of our review process is
to
assist you in your compliance with the applicable disclosure
requirements and to enhance the overall disclosure in your
filings.
We look forward to working with you in these respects.  We welcome
any questions you may have about our comments or on any other
aspect
of our review.  Feel free to call us at the telephone numbers
listed
at the end of this letter.

Aon Corp. Form 10-K for the year ended December 31, 2004

General

We note from Exhibit 21 to the Company`s Form 10-K for the fiscal
year-ended December 31, 2004, that the Company has two foreign
subsidiaries in Iran - Mahamy Company plc (Aon Iran) and United
Iranian Insurance Services plc Tehran.  In view of the fact that
Iran
has been identified by the U.S. State Department as a state
sponsor
of terrorism, and is subject to economic sanctions administered by
the U.S. Treasury Department`s Office of Foreign Assets Control,
please advise us of the materiality to the Company of its
operations
in Iran, and give us your view as to whether those operations
constitute a material investment risk for your security holders.
In
preparing your response, please consider that evaluations of
materiality should not be based solely on quantitative factors,
but
should include consideration of all factors, including the
potential
impact of corporate activities upon a company`s reputation and
share
value, that a reasonable investor would deem important in making
an
investment decision.
Closing

      Please understand that we may have additional comments after
we
review your response to our comment.  Please contact Franklin
Green
at (202) 942-4747 if you have any questions about the comment or
our
review.  You may also contact me at (202) 942-7817.

Sincerely,



		Cecilia D. Blye, Chief
		Office of Global Security Risk


cc: 	Jeffrey Riedler
		Assistant Director
		Division of Corporation Finance

Patrick Ryan
Chairman
April 28, 2005
Page 1




UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549-0404

         DIVISION OF
CORPORATION FINANCE