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.

Darby Creek is a tributary of the Delaware River in Chester, Delaware and Philadelphia counties, in the U.S. Commonwealth of Pennsylvania. It is approximately 26 miles (42 km) long. The watershed of the creek has an area of 77.2 square miles (200 km2). It has twelve named direct tributaries, including Cobbs Creek, Little Darby Creek, Ithan Creek, and Muckinipattis Creek. The creek has a low level of water quality for most of its length. The lower Darby Creek area was deemed a Superfund site by the U.S. Environmental Protection Agency (EPA) due to contamination with dangerous chemicals from two landfills.