Upper Darby Township, often shortened to Upper Darby, is a home rule township in Delaware County, Pennsylvania, United States. As of the 2020 census, the township had a total population of 85,681, making it the state's sixth-most populated municipality after Philadelphia, Pittsburgh, Allentown, Reading, and Erie. Upper Darby borders Philadelphia, the nation's sixth-most populous city, and constitutes part of the Delaware Valley, also known as the Philadelphia metropolitan area, the nation's seventh-largest metropolitan area.