<PAGE>
Exhibit 24
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ PATRICK G. RYAN
-------------------
Patrick G. Ryan
1
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ DANIEL T. CARROLL
---------------------
Daniel T. Carroll
2
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ FRANKLIN A. COLE
--------------------
Franklin A. Cole
3
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ EDGAR D. JANNOTTA
---------------------
Edgar D. Jannotta
4
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ LESTER B. KNIGHT
--------------------
Lester B. Knight
5
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ PERRY J. LEWIS
------------------
Perry J. Lewis
6
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ ANDREW J. McKENNA
---------------------
Andrew J. McKenna
7
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ NEWTON N. MINOW
-------------------
Newton N. Minow
8
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ RICHARD C. NOTEBAERT
------------------------
Richard C. Notebaert
9
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ MICHAEL D. O'HALLERAN
-------------------------
Michael D. O'Halleran
10
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ DONALD S. PERKINS
---------------------
Donald S. Perkins
11
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ JOHN W. ROGERS, JR.
-----------------------
John W. Rogers, Jr.
12
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ GEORGE A. SCHAEFER
----------------------
George A. Schaefer
13
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ RAYMOND I. SKILLING
-----------------------
Raymond I. Skilling
14
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ FRED L. TURNER
------------------
Fred L. Turner
15
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ ARNOLD R. WEBER
-------------------
Arnold R. Weber
16
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ CAROLYN Y. WOO
------------------
Carolyn Y. Woo
17
<PAGE>
POWER OF ATTORNEY
-----------------
KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears
below constitutes and appoints Patrick G. Ryan, Harvey N. Medvin and Raymond I.
Skilling, and each of them, with full power to act without the others, his true
and lawful attorneys-in-fact and agents, with full and several power of
substitution and resubstitution for him and in his name, place and stead, in any
and all capacities, to sign a registration statement on Form S-3 relating to the
registration by Aon Corporation of up to 4,700,000 shares of common stock and
any and all amendments (including post-effective amendments) to such
registration statement, and to file the same, with all exhibits thereto, and
other documents in connection therewith, with the Securities and Exchange
Commission, and any documents relating to the qualification or registration
under state Blue Sky or securities laws of such securities, granting unto such
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or their or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.
IN WITNESS WHEREOF, the undersigned has signed his name this 14th day of
July, 2000.
/s/ HARVEY N. MEDVIN
--------------------
Harvey N. Medvin
18
