**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 FinancialOfficer of 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 thecircumstances under which such statements were made, notmisleading with respect to the period covered by this report; 3. Based on my knowledge, the financial statements, and otherfinancial information included in this report, fairly present inall material respects the financial condition, results ofoperations and cash flows of the registrant as of, and for, theperiods presented in this report; 4. The registrant’s other certifying officer(s) and I are responsiblefor establishing and maintaining disclosure controls andprocedures (as defined in Exchange Act Rules 13a-15(e) and15d-15(e)) and internal control over financial reporting (asdefined in Exchange Act Rules 13a-15(f) and 15d-15(f) for theregistrant and have: a) designed such disclosure controls and procedures, orcaused such disclosure controls and procedures to bedesigned under our supervision, to ensure thatmaterial information relating to the registrant,including its consolidated subsidiaries, is made knownto us by others within those entities, particularlyduring the period in which this report is beingprepared;  b) designed such internal control over financialreporting, or caused such internal control overfinancial reporting to be designed under oursupervision, to provide reasonable assurance regardingthe reliability of financial reporting and thepreparation of financial statements for externalpurposes in accordance with generally acceptedaccounting principles;  c) evaluated the effectiveness of the registrant’sdisclosure controls and procedures and presented inthis report our conclusions about the effectiveness ofthe disclosure controls and procedures, as of the endof the period covered by this report based on suchevaluation; and  d) disclosed in this report any change in theregistrant’s internal control over financial reportingthat occurred during the registrant’s most recentfiscal quarter (the registrant’s fourth fiscal quarterin the case of an annual report) that has materiallyaffected, or is reasonably likely to materiallyaffect, the registrant’s internal control overfinancial reporting; and5. The registrant’s other certifying officer(s) and I have disclosed,based on our most recent evaluation of internal control overfinancial reporting, to the registrant’s auditors and the auditcommittee of the registrant’s board of directors (or personsperforming the equivalent functions): a) all significant deficiencies and material weaknessesin the design or operation of internal control overfinancial reporting which are reasonably likely toadversely affect the registrant’s ability to record,process, summarize and report financial information;and  b) any fraud, whether or not material, that involvesmanagement or other employees who have a significantrole in the registrant’s internal control overfinancial reporting.Date: May 10, 2007   /s/ Michael P. McGrath Michael P. McGrath  Executive Vice President, Treasurer, Secretary     and Chief Financial Officer  
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