<PAGE>

                                                                      Exhibit 24

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and
appoints John C. Rosengren his true and lawful attorney-in-fact and agent, with
full power of substitution and resubstitution, for him, and in his name, place
and stead, in any and all capacities (i) to sign a registration statement on
Form S-4 and any and all amendments (including post-effective amendments) to
such registration statement to be filed by Arthur J. Gallagher & Co. and
relating to shares of its Common Stock and (ii) 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 said attorney-in-fact and agent full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in such connection, as fully to all intents and purposes as the
undersigned might or could do in person, hereby ratifying and confirming all
that said attorney-in-fact and agent, or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.

     IN WITNESS WHEREOF, the undersigned has duly executed this instrument as of
this 7/th/ day of March, 2002.

                                                   /s/ Robert E. Gallagher
                                                 -------------------------------





<PAGE>

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and
appoints John C. Rosengren his true and lawful attorney-in-fact and agent, with
full power of substitution and resubstitution, for him, and in his name, place
and stead, in any and all capacities (i) to sign a registration statement on
Form S-4 and any and all amendments (including post-effective amendments) to
such registration statement to be filed by Arthur J. Gallagher & Co. and
relating to shares of its Common Stock and (ii) 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 said attorney-in-fact and agent full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in such connection, as fully to all intents and purposes as the
undersigned might or could do in person, hereby ratifying and confirming all
that said attorney-in-fact and agent, or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.

     IN WITNESS WHEREOF, the undersigned has duly executed this instrument as of
this 7/th/ day of March, 2002.

                                                /s/ James J. Braniff III
                                              ----------------------------------




<PAGE>

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and
appoints John C. Rosengren his true and lawful attorney-in-fact and agent, with
full power of substitution and resubstitution, for him, and in his name, place
and stead, in any and all capacities (i) to sign a registration statement on
Form S-4 and any and all amendments (including post-effective amendments) to
such registration statement to be filed by Arthur J. Gallagher & Co. and
relating to shares of its Common Stock and (ii) 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 said attorney-in-fact and agent full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in such connection, as fully to all intents and purposes as the
undersigned might or could do in person, hereby ratifying and confirming all
that said attorney-in-fact and agent, or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.

     IN WITNESS WHEREOF, the undersigned has duly executed this instrument as of
this 7/th/ day of March, 2002.

                                              /s/ T. Kimball Brooker
                                            ------------------------------------




<PAGE>

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and
appoints John C. Rosengren his true and lawful attorney-in-fact and agent, with
full power of substitution and resubstitution, for him, and in his name, place
and stead, in any and all capacities (i) to sign a registration statement on
Form S-4 and any and all amendments (including post-effective amendments) to
such registration statement to be filed by Arthur J. Gallagher & Co. and
relating to shares of its Common Stock and (ii) 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 said attorney-in-fact and agent full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in such connection, as fully to all intents and purposes as the
undersigned might or could do in person, hereby ratifying and confirming all
that said attorney-in-fact and agent, or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.

     IN WITNESS WHEREOF, the undersigned has duly executed this instrument as of
this 7/th/ day of March, 2002.

                                                    /s/ Gary P. Coughlan
                                                  ------------------------------




<PAGE>

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and
appoints John C. Rosengren his true and lawful attorney-in-fact and agent, with
full power of substitution and resubstitution, for him, and in his name, place
and stead, in any and all capacities (i) to sign a registration statement on
Form S-4 and any and all amendments (including post-effective amendments) to
such registration statement to be filed by Arthur J. Gallagher & Co. and
relating to shares of its Common Stock and (ii) 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 said attorney-in-fact and agent full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in such connection, as fully to all intents and purposes as the
undersigned might or could do in person, hereby ratifying and confirming all
that said attorney-in-fact and agent, or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.

     IN WITNESS WHEREOF, the undersigned has duly executed this instrument as of
this 7/th/ day of March, 2002.

                                                /s/ James W. Durkin, Jr.
                                             -----------------------------------




<PAGE>

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and
appoints John C. Rosengren her true and lawful attorney-in-fact and agent, with
full power of substitution and resubstitution, for her, and in her name, place
and stead, in any and all capacities (i) to sign a registration statement on
Form S-4 and any and all amendments (including post-effective amendments) to
such registration statement to be filed by Arthur J. Gallagher & Co. and
relating to shares of its Common Stock and (ii) 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 said attorney-in-fact and agent full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in such connection, as fully to all intents and purposes as the
undersigned might or could do in person, hereby ratifying and confirming all
that said attorney-in-fact and agent, or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.

     IN WITNESS WHEREOF, the undersigned has duly executed this instrument as of
this 7/th/ day of March, 2002.

                                                     /s/ Ilene S. Gordon
                                                   -----------------------------




<PAGE>

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and
appoints John C. Rosengren his true and lawful attorney-in-fact and agent, with
full power of substitution and resubstitution, for him, and in his name, place
and stead, in any and all capacities (i) to sign a registration statement on
Form S-4 and any and all amendments (including post-effective amendments) to
such registration statement to be filed by Arthur J. Gallagher & Co. and
relating to shares of its Common Stock and (ii) 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 said attorney-in-fact and agent full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in such connection, as fully to all intents and purposes as the
undersigned might or could do in person, hereby ratifying and confirming all
that said attorney-in-fact and agent, or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.

     IN WITNESS WHEREOF, the undersigned has duly executed this instrument as of
this 7/th/ day of March, 2002.

                                                   /s/ David E. McGurn, Jr.
                                                --------------------------------




<PAGE>

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and
appoints John C. Rosengren his true and lawful attorney-in-fact and agent, with
full power of substitution and resubstitution, for him, and in his name, place
and stead, in any and all capacities (i) to sign a registration statement on
Form S-4 and any and all amendments (including post-effective amendments) to
such registration statement to be filed by Arthur J. Gallagher & Co. and
relating to shares of its Common Stock and (ii) 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 said attorney-in-fact and agent full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in such connection, as fully to all intents and purposes as the
undersigned might or could do in person, hereby ratifying and confirming all
that said attorney-in-fact and agent, or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.

     IN WITNESS WHEREOF, the undersigned has duly executed this instrument as of
this 7/th/ day of March, 2002.

                                                  /s/ Richard J. McKenna
                                               ---------------------------------




<PAGE>

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and
appoints John C. Rosengren his true and lawful attorney-in-fact and agent, with
full power of substitution and resubstitution, for him, and in his name, place
and stead, in any and all capacities (i) to sign a registration statement on
Form S-4 and any and all amendments (including post-effective amendments) to
such registration statement to be filed by Arthur J. Gallagher & Co. and
relating to shares of its Common Stock and (ii) 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 said attorney-in-fact and agent full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in such connection, as fully to all intents and purposes as the
undersigned might or could do in person, hereby ratifying and confirming all
that said attorney-in-fact and agent, or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.

     IN WITNESS WHEREOF, the undersigned has duly executed this instrument as of
this 7/th/ day of March, 2002.

                                                 /s/ Robert Ripp
                                               ---------------------------------




<PAGE>

                                POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and
appoints John C. Rosengren his true and lawful attorney-in-fact and agent, with
full power of substitution and resubstitution, for him, and in his name, place
and stead, in any and all capacities (i) to sign a registration statement on
Form S-4 and any and all amendments (including post-effective amendments) to
such registration statement to be filed by Arthur J. Gallagher & Co. and
relating to shares of its Common Stock and (ii) 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 said attorney-in-fact and agent full power and
authority to do and perform each and every act and thing requisite and necessary
to be done in such connection, as fully to all intents and purposes as the
undersigned might or could do in person, hereby ratifying and confirming all
that said attorney-in-fact and agent, or his substitute or substitutes, may
lawfully do or cause to be done by virtue hereof.

     IN WITNESS WHEREOF, the undersigned has duly executed this instrument as of
this 7/th/ day of March, 2002.


                                                     /s/ James R. Wimmer
                                                  ------------------------------








