16 Pa. Stat. § 5821
The county commissioners of any county may take charge of or rebuild and reconstruct any bridge owned and maintained by corporations where the same has been destroyed by ice or otherwise, within ten years, or abandoned by the owners, where such bridge crosses any stream or river running into or through such county.
Any bridge used exclusively for vehicles and foot purposes, over any stream or river forming the boundary line between two counties, being on the line of a public highway, or deemed necessary for the use of the traveling public, and owned and maintained by corporations or by private persons, or which was built by public subscriptions, which has been destroyed by ice, flood or otherwise, at any time, or which has been or may be abandoned and the site or location and piers and abutments no longer used by the owners, may be rebuilt and maintained jointly as a county bridge by the county commissioners of such counties, and the costs and expenses of such joint reconstruction shall be paid by the said counties respectively in the proportion of the population thereof, as ascertained at the last census.
16 P.S. § 5821