The Mispillion River is a river flowing to Delaware Bay in southern Delaware in the United States. It is approximately 15 miles (24 km) long and drains an area of 76 square miles (197 km2) on the Atlantic Coastal Plain. A boardwalk known as the Mispillion Riverwalk follows the river in Milford. As of 2003, an effort was underway to preserve a greenway along the river upstream and downstream of Milford.