16 Pa. Stat. § 3409
In case of a vacancy happening by death, resignation or otherwise in any county office created by the Constitution or laws of this Commonwealth, and where no other provision is made by the Constitution or by the provisions of this act to fill the vacancy, it shall be the duty of the Governor to appoint a suitable person to fill such office, who shall continue therein and discharge the duties thereof until the first Monday of January next succeeding the first municipal election which shall occur two or more months after the happening of such vacancy in counties of the second class. In counties of the second class A the appointed person shall continue therein and discharge the duties thereof for the balance of the unexpired term. Such appointee shall be confirmed by the Senate if in session.
16 P.S. § 3409