The Mackinac Straits is the strip of water that connects two of the Great Lakes, Lake Michigan and Lake Huron and separates the Lower Peninsula of Michigan from the Upper Peninsula of Michigan. It is a shipping lane connecting, for instance, the steel mills of Gary, Indiana to the iron mines of Minnesota. Before the railroads reached Chicago from the east, it served as part of the path for immigrants into the Midwest and Great Plains. It is five miles wide (over 8 km) at its narrowest point where it is spanned by the Mackinac Bridge. Before the bridge was built, car ferries were used to cross the straits. Today passenger-only ferries carry people to Mackinac Island which does not permit cars. Before icebreakers and year-round shipping on the Lower Great Lakes, the Straits would freeze over in winter.

The Straits were an important Native American and fur trade route. Located on the southern side of the straights is the town of Mackinaw City, Michigan, formerly the site of Fort Michilimackinac, a French fort, and on the northern side is St. Ignace, Michigan, site of a French Catholic mission to the Indians, founded in 1671. The eastern end of the Straits was controlled by Fort Mackinac on Mackinac Island, a British colonial and early American military base and fur trade center.