16 Pa. Stat. § 7171
Where a part of the county, or a borough which constitutes a part of a county, is so located that it is to the best interest of such part of a county or borough so located and of the inhabitants thereof and of the inhabitants of the adjoining county or city that such part of a county or borough be annexed to an adjoining county, the court of quarter sessions of the county wherein such part or borough is then situate may on petition decree such alterations of the boundaries of the county as shall be for the best interest of the inhabitants aforesaid and of the inhabitants of the adjoining county or city. The term "part of county," as used in this act, shall not include an area greater than two hundred and fifty acres nor an area containing a population of over two thousand inhabitants.
16 P.S. § 7171