25 Pa. Stat. § 236
The qualified voters of every election district, in boroughs and townships in the Commonwealth of Pennsylvania wherein more than one election district is authorized, and where but one assessor for valuation of taxable property resides in the borough or township having more than one election district, shall, at the next municipal election and every four years thereafter, elect a properly qualified person for assistant assessor in each of said election districts, who shall perform all the duties relating to elections now required to be performed by assessors in boroughs and townships having but one election district.
In case of a vacancy in said office, the court of quarter sessions, or any judge of the said court of the same county, shall appoint a person to fill such vacancy.
25 P.S. § 236