|St. Joseph River|
Map of the Maumee River watershed showing the St. Joseph River.
|Main source||Hillsdale County, Michigan
856 ft (261 m)
|River mouth||Maumee River, Ft. Wayne, Indiana
751 ft (229 m)
|Length||100 mi (160 km)|
The St. Joseph River is an 86.1-mile-long (138.6 km) tributary of the Maumee River in northwestern Ohio, and northeastern Indiana in the United States, with headwater tributaries rising in southern Michigan. It drains a primarily rural farming region in the watershed of Lake Erie. It shares its name with the St. Joseph River of Lake Michigan, but the two rivers flow in generally opposite directions.
At the end of the Wisconsin glaciation, the glacier's Erie Lobe retreated toward the northeast, leaving large debris deposits called moraines. The St. Joseph formed as a meltwater channel between the north limbs of two of these moraines, the Wabash Moraine on the west and the Fort Wayne Moraine on the east. At that time it joined the St. Marys River to drain into the Wabash River. Later, the shrinkage of Glacial Lake Maumee, the ancestor of modern Lake Erie, brought about the opening of the modern Maumee River, which captured the flow of the St. Joseph and the St. Marys, causing the St. Marys to reverse its course to meet the flow of the St. Joseph almost head-on.
The St. Joseph River forms in northern Williams County, Ohio, at the confluence of the East and West branches at  Both branches rise in southern Hillsdale County, Michigan. The headwaters of the East Branch are within 3 miles (4.8 km) of those of the St. Joseph River of Lake Michigan. Both branches initially flow southeast, then turn to the southwest to flow across the northwestern corner of Ohio past Montpelier. The St. Joseph enters De Kalb County in northeastern Indiana, flowing southwest past Saint Joe and into the city of Fort Wayne, where it meets the St. Marys River to form the Maumee River at .
From the mouth:
The St. Joseph River and tributaries drain all or portions of the following: