16 Pa.C.S. § 12504: Quorum and execution of official instruments.

(a) Quorum.--The county commissioners shall constitute a board, two members of which shall be a quorum for the transaction of business and, when convened after notice, shall be competent to perform each of the duties pertaining to the office of county commissioners.

(b) Execution.--If an official document, instrument or official paper is to be executed by the county commissioners, the execution shall be done by at least two of the county commissioners and attested by the chief clerk who shall affix the county seal to the document.