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.

Delaware County, colloquially referred to as Delco, is a county in the Commonwealth of Pennsylvania. With a population of 576,830 as of the 2020 census, it is the fifth-most populous county in Pennsylvania and the third-smallest in area. The county was created on September 26, 1789, from part of Chester County and named for the Delaware River. The county is part of the Southeast Pennsylvania region of the state.