The Fox River is a river in eastern Wisconsin in the Great Lakes region of the United States. It is the principal tributary of Green Bay, and via the Bay, the largest tributary of Lake Michigan. The city of Green Bay, one of the first European settlements in the interior of North America, is on the river at its mouth on lower Green Bay.

Green Bay is an arm of Lake Michigan, located along the south coast of Michigan's Upper Peninsula and the east coast of Wisconsin. It is separated from the rest of the lake by the Door Peninsula in Wisconsin, the Garden Peninsula in Michigan, and the chain of islands between them, all formed by the Niagara Escarpment. Green Bay is some 120 miles (193 km) long, with a width ranging from about 10 to 20 miles ; it is 1,626 square miles (4,210 km2) in area.