Exhibit 24

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ Gregory C. Case

Gregory C. Case

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ Patrick G. Ryan

Patrick G. Ryan

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ Edgar D. Jannotta

Edgar D. Jannotta

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ Jan Kalff

Jan Kalff

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ Lester B. Knight

Lester B. Knight

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ J. Michael Losh

J. Michael Losh

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ R. Eden Martin

R. Eden Martin

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ Andrew J. McKenna

Andrew J. McKenna

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ Robert S. Morrison

Robert S. Morrison

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ Richard B. Myers

Richard B. Myers

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ Richard C. Notebaert

Richard C. Notebaert

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ John W. Rogers, Jr.

John W. Rogers, Jr.

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ Gloria Santona

Gloria Santona

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, David P. Bolger and D. Cameron Findlay and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with respect to the registration under the Securities Act of securities and obligations of Aon Corporation with respect to its Stock Incentive Plan, and any and all amendments and supplements thereto (including all pre-effective and post-effective amendments), and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, 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 to the end that such Registration Statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of July 20, 2007.

/s/ Carolyn Y. Woo

Carolyn Y. Woo