Exhibit 31.2
   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 untrue
statement of a material fact or omit to state a material fact
necessary to make the statements made, in light of the
circumstances under which such statements were made, not
misleading with respect to the period covered by this report;3.
    
    Based on my knowledge, the financial statements, and other
financial information included in this report, fairly present in
all material respects the financial condition, results of
operations and cash flows of the registrant as of, and for, the
periods presented in this report;4.
    
    The registrants other certifying officer(s) and I are responsible
for establishing and maintaining disclosure controls and
procedures (as defined in Exchange Act Rules 13a-15(e) and
15d-15(e)) and internal control over financial reporting (as
defined in Exchange Act Rules 13a-15(f) and 15d-15(f) for the
registrant and have:
 a)
    
    designed such disclosure controls and procedures, or caused such
disclosure controls and procedures to be designed under our
supervision, to ensure that material information relating to the
registrant, including its consolidated subsidiaries, is made known
to us by others within those entities, particularly during the
period in which this report is being prepared;b)
    
    designed such internal control over financial
reporting, or caused such internal control over
financial reporting to be designed under our
supervision, to provide reasonable assurance regarding
the reliability of financial reporting and the
preparation of financial statements for external
purposes in accordance with generally accepted
accounting principles;c)
    
    evaluated the effectiveness of the registrants
disclosure controls and procedures and presented in
this report our conclusions about the effectiveness of
the disclosure controls and procedures, as of the end
of the period covered by this report based on such
evaluation; andd)
    
    disclosed in this report any change in the registrants internal
control over financial reporting that occurred during the
registrants most recent fiscal quarter (the registrants fourth
fiscal quarter in the case of an annual report) that has
materially affected, or is reasonably likely to materially affect,
the registrants internal control over financial reporting; and
 5.
    
    The registrants other certifying officer(s) and I have disclosed,
based on our most recent evaluation of internal control over
financial reporting, to the registrants auditors and the audit
committee of the registrants board of directors (or persons
performing the equivalent functions):
 a)
    
    all significant deficiencies and material weaknesses in the design
or operation of internal control over financial reporting which
are reasonably likely to adversely affect the registrants ability
to record, process, summarize and report financial information;
andb)
    
    any fraud, whether or not material, that involves management or
other employees who have a significant role in the registrants
internal control over financial reporting.
  /s/ Michael P. McGrathMichael P. McGrathExecutive Vice President, Treasurer, Secretary
and Chief Financial Officer