river in north-central United States that rises near Hillsdale in south-central Michigan and flows generally west but swings south into northern Indiana, through Elkhart and South Bend, before reentering Michigan to empty into Lake Michigan at Saint Joseph and Benton Harbor. The Saint Joseph River, 210 miles (340 km) long, has been dammed at Union City, Michigan, for hydroelectric development and is an important source of urban and industrial water supply.

The river is not to be confused with another Saint Joseph River, which also rises near Hillsdale and flows generally south for 100 miles (160 km) through Michigan and Ohio to form the Maumee River in Indiana.