The St. Joseph River is a tributary of Lake Michigan with a length of 206 miles (332 km). The river flows in a generally westerly direction through southern Michigan and northern Indiana, United States, to its terminus on the southeast shore of the lake. It drains a primarily rural farming area in the watershed of Lake Michigan. It was enormously important to Native Americans and greatly aided in the colonial exploration, settlement and administration of New France and the nascent United States as a canoe route between Lake Michigan and the watershed of the Mississippi River.

Lake Michigan is one of the five Great Lakes of North America. It is the second-largest of the Great Lakes by volume and the third-largest by surface area, after Lake Superior and Lake Huron. To the east, its basin is conjoined with that of Lake Huron through the 3+1⁄2-mile (5.6-kilometer) wide, 295-foot deep Straits of Mackinac, giving it the same surface elevation as its easterly counterpart; geologically, the two bodies are a single lake that is, by area, the largest freshwater lake in the world.