The original Lower St. Clair Township consisted of the present-day neighborhoods of the City of Pittsburgh south of the Monongahela and Ohio, and all or parts of Green Tree, Carnegie, Baldwin, Bridgeville, Dormont, Mount Lebanon and other boroughs and townships in the South Hills.
Initially, Lower St. Clair Township encompassed the areas now part of the City of Pittsburgh south of the Monongahela and Ohio rivers, as well as sections or entirety of Green Tree, Carnegie, Baldwin, Bridgeville, Dormont, Mount Lebanon, and surrounding communities in the South Hills.