The Nanticoke River is a major tributary of the Chesapeake Bay on the Delmarva Peninsula. It rises in southern Kent County, Delaware, flows through Sussex County, Delaware, and forms the boundary between Dorchester County, Maryland and Wicomico County, Maryland. The tidal river course proceeds southwest into the Tangier Sound, Chesapeake Bay. The river is 64.3 miles (103.5 km) long.