Darby Creek (historically known as Church Creek or the Derby River) is a tributary of the Delaware River in Chester County, Delaware County, and Philadelphia County, in Pennsylvania, in the United States. 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.