72 Pa. Stat. § 5020-412
Where seated lands are divided by the boundary line between a township and a city, borough or town, and the mansion house is situate in a township, the whole of such lands shall be assessed only in the township where the mansion house is situated. Where the mansion house is situated in a city, borough or town, and the balance of such seated lands are located in one or more townships, the land located in such township or townships shall be assessed therein, and the land located in the city, borough or town shall be assessed therein.
Where seated lands are divided by the boundary line between two townships, the land located in each township shall be assessed therein, notwithstanding the situs of the residence or mansion house.
72 P.S. § 5020-412