**Exhibit 31.2**Certification Pursuant to Section 302 of the Sarbanes-Oxley Act of 2002I, Michael P. McGrath, Executive Vice President, Treasurer, Secretary and Chief Financial Officerof the registrant, certify that:1. I have reviewed this quarterly report on Form 10-Q of Mercantile Bancorp, Inc.; 2. Based on my knowledge, this report does not contain any untruestatement of a material fact or omit to state a material factnecessary to make the statements made, in light of the circumstancesunder which such statements were made, not misleading with respect tothe period covered by this report; 3. Based on my knowledge, the financial statements, and other financialinformation included in this report, fairly present in all materialrespects the financial condition, results of operations and cash flowsof the registrant as of, and for, the periods presented in thisreport; 4. The registrant’s other certifying officers and I are responsible forestablishing and maintaining disclosure controls and procedures (asdefined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internalcontrol over financial reporting (as defined in Exchange Act Rules13a-15(f) and 15d-15(f)) for the registrant and have: a) designed such disclosure controls and procedures, or caused suchdisclosure controls and procedures to be designed under oursupervision, to ensure that material information relating to theregistrant, including its consolidated subsidiaries, is made known tous by others within those entities, particularly during the period inwhich this report is being prepared;  b) designed such internal control over financial reporting, or causedsuch internal control over financial reporting to be designed underour supervision, to provide reasonable assurance regarding thereliability of financial reporting and the preparation of financialstatements for external purposes in accordance with generally acceptedaccounting principles;  c) evaluated the effectiveness of the registrant’s disclosure controlsand procedures and presented in this report our conclusions about theeffectiveness of the disclosure controls and procedures, as of the endof the period covered by this report based on such evaluation; and  d) disclosed in this report any change in the registrant’s internalcontrol over financial reporting that occurred during the registrant’smost recent fiscal quarter (the registrant’s fourth fiscal quarter inthe case of an annual report) that has materially affected, or isreasonably likely to materially affect, the registrant’s internalcontrol over financial reporting; and5. The registrant’s other certifying officer(s) and I have disclosed,based on our most recent evaluation of internal control over financialreporting, to the registrant’s auditors and the audit committee of theregistrant’s board of directors (or persons performing the equivalentfunctions): a) all significant deficiencies and material weaknesses in the design oroperation of internal control over financial reporting which arereasonably likely to adversely affect the registrant’s ability torecord, process, summarize and report financial information; and  b) any fraud, whether or not material, that involves management or otheremployees who have a significant role in the registrant’s internalcontrol over financial reporting.Date: November 8, 2007        /s/ Michael P. McGrath  Michael P. McGrath  Executive Vice President, Treasurer, Secretary and