**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 officers 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, 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 knownto us by others within those entities, particularly during theperiod in which 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 theregistrant’s most recent fiscal quarter (the registrant’s fourthfiscal quarter in the case of an annual report) that hasmaterially affected, or is reasonably likely to materially affect,the registrant’s internal control over financial 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 weaknesses in the designor operation of internal control over financial reporting whichare reasonably likely to adversely affect the registrant’s abilityto record, process, summarize and report financial information;and  b) any fraud, whether or not material, that involves management orother employees who have a significant role in the registrant’sinternal control over financial reporting.   Date: August 9, 2007     /s/ Michael P. McGrath   Michael P. McGrath  Executive Vice President, Treasurer, Secretary  and Chief Financial Officer