 Philadelphia County is part of the Philadelphia-Camden-Wilmington, PA-NJ-DE-MD (Combined Statistical Area, known as the Delaware Valley), located along the lower Delaware and Schuylkill Rivers, within the Northeast megalopolis.Philadelphia County is the economic and cultural anchor of the Delaware Valley, the eighth-largest combined statistical area in the United States, with a population of 7.2 million.Native American tribes of Lenape were the first known occupants in the area that became Philadelphia County.