53 Pa. Stat. § 1336
In each county in this Commonwealth where the county-seat is within the limits of any city, the county commissioners and the corporate authorities of such city shall have the power, and they are hereby authorized, to agree upon a site within the limits of such city, to acquire, own and hold the same as tenants in common, and to erect thereon a joint county and municipal building or buildings, to be used by the county for courthouse and other county purposes and by the city for municipal purposes. The county commissioners and the corporate authorities of such city shall agree upon and adopt plans for such building or buildings, and, upon the approval of such plans by the court of common pleas of such county, the county commissioners and the corporate authorities of such city shall have full authority to erect, upon the land thus obtained and held, the building or buildings so adopted and approved.
53 P.S. § 1336