The Fox River is a 202-mile-long (325 km) tributary of the Illinois River, flowing from southeastern Wisconsin to Ottawa, Illinois in the United States. The Wisconsin section was known as the Pishtaka River in the 19th century. There is another Fox River in Wisconsin that flows through Lake Winnebago into Green Bay. There are also two other "Fox Rivers" in southern Illinois: the Fox River and a smaller "Fox River" that joins the Wabash River near New Harmony, Indiana.

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.