53 Pa. Stat. § 1334
If it shall be deemed necessary to acquire additional land for such site, the county, in case the site is chosen on the land of the county, or if the site chosen is on the land of the city, then the city, is authorized and empowered to acquire by purchase or condemnation such additional land. The right of eminent domain herein conferred upon the county shall be exercised in the manner provided by the act of Assembly of June first, one thousand eight hundred and eighty-three, authorizing the county commissioners of any county to acquire ground at the county-seat for the purpose of the erection or extension of such building as may be necessary for the accommodation of the courts and the several officers of the county. The right of eminent domain herein conferred upon the city shall be exercised in the manner provided by law for the acquisition of real estate within the city limits for the erection of municipal buildings.
53 P.S. § 1334