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.