<PAGE>

                                                                    EXHIBIT 31.1

CERTIFICATION PURSUANT TO
18 U.S.C. SECTION 1350
AS ADOPTED PURSUANT TO
SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002

CERTIFICATIONS

I, Thomas F. Rokisky, certify that:

1.   I have reviewed this quarterly report on Form 10-Q of CNB Financial
     Services, 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
     quarterly 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 and I are responsible for
     establishing and maintaining disclosure controls and procedures (as defined
     in Exchange Act Rules 13a-15e and 15d-15e) 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 quarterly report
               our conclusions about the effectiveness of the disclosure
               controls and procedures, as of the end of the period covered by
               this quarterly report based on such evaluation; and

          d.   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 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 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; and

          b.   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 report.


Date: August 14, 2008                   /s/ Thomas F. Rokisky
                                        ----------------------------------------
                                        [Signature]
                                        [Title]


                                       29