 Fairmount Park, when combined with Wissahickon Valley Park, is one of the largest contiguous urban park areas in the United States.The two parks, along with the Colonial Revival, Georgian and Federal-style mansions contained in them, have been listed as one entity on the National Register of Historic Places since 1972.From a governmental perspective, Philadelphia County is a legal nullity, as all county functions were assumed by the city in 1952.