53 Pa. Stat. § 1337
It shall be lawful, and the county commissioners and the corporate authorities of such city are hereby authorized and empowered, to choose, for the site of such joint county and municipal building or buildings, land owned and held by the county, or land owned and held by the city. Whenever the site, chosen as aforesaid, consists of land owned and held by the county, it shall be lawful for the county commissioners of such county, and they are hereby authorized and empowered, to convey in fee to such city, at private sale and upon a fair valuation, such an undivided interest therein as may be agreed upon. It shall be lawful for the corporate authorities of such city, and they are hereby authorized and empowered, to pay in cash for such undivided interest, or, in their discretion, to convey in fee to the county, at private sale and at a fair valuation, in exchange for the conveyance to the city of the undivided interest aforesaid, any land owned by the city which, in the estimation of the corporate authorities of such city, is not needed for municipal purposes. The land, or any part thereof, so conveyed to the county, may be held and used by the county for county purposes, or, if in the estimation of the county commissioners it is not needed for such purposes, it may be sold by the county commissioners at either public or private sale.
Whenever the site, chosen as aforesaid, consists of land owned and held by the city, it shall be lawful for the corporate authorities of such city, and they are hereby authorized and empowered, to convey in fee to such county, at private sale and upon a fair valuation, such an undivided interest therein as may be agreed upon. It shall also be lawful for the county commissioners of such county, and they are hereby authorized and empowered, to pay in cash for such undivided interest, or, in their discretion, to convey in fee to the city, at private sale and upon a fair valuation, in exchange for the conveyance to the county of the undivided interest aforesaid, any land owned by the county which, in the estimation of the county commissioners, is not needed for county purposes. The land, or any part thereof, so conveyed to the city, may be held and used by the city for municipal purposes, or, if in the estimation of the corporate authorities of such city it is not needed for such purposes, it may be sold by the corporate authorities of such city at either public or private sale.
53 P.S. § 1337