EXHIBIT 32.2

Certification Pursuant to 18 U.S.C. Section 1350, as adopted pursuant to

Section 906 of the Sarbanes-Oxley Act of 2002

In connection with the quarterly report of Mercantile Bancorp, Inc. (the “Company”) on Form 10-Q for the period ending June 30, 2011 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Michael P. McGrath, Executive Vice President, Treasurer, Secretary and Chief Financial Officer of the Company, certify, pursuant to Rule 13a-14(b) of the Securities Exchange Act of 1934, as amended, and 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

1. The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

2. The information contained in the report fairly presents, in all material respects, the financial condition and operating results of the Company.

/s/ Michael P. McGrath                                               

Michael P. McGrath

Executive Vice President, Treasurer, Secretary
and Chief Financial Officer

Date: August 15, 2011