Wisconsin's area of 56,066 square miles, in the north central portion of the United States, is defined by a ragged boundary. Lake Michigan lies on the east, Lake Superior and the Menominee, Brule, and Montreal Rivers on the north, the St. Louis, St. Croix, and Mississippi Rivers on the west. Only the southern border and some relatively few miles at the State's northern limits follow a line unsuggested by natural water courses.
The topography today is essentially the same as it was immediately following the Ice Age. Broadly, it may be described as a composite of large areas of plains, smaller areas of stream-cut plateaus, and large areas of erosion-worn mountains. Elevations above sea level range between 581 feet where Wisconsin's eastern border edges Lake Michigan to a highest point of 1,940 feet at Rib Mountain near Wausau. The mean altitude for Wisconsin is 1,050 feet. Generally speaking, the elevation of the north is higher than that of the rest of the State.
Streams to the west of Wisconsin's major watershed, a broad land arch extending north and south through the middle of the State, empty by way of the Mississippi River into the Gulf of Mexico. Chief among these streams are the St. Croix, Chippewa, Black, and Wisconsin Rivers, the latter the State's largest interior waterway. Each joins the Mississippi at some point along Wisconsin's western border. The Rock River and some few small streams flow through Wisconsin into Illinois, where they join the Mississippi system. Streams to the east of the watershed. empty into the Atlantic Ocean by way of Lake Superior or Lake Michigan. The St. Louis, Brule, Bad, Nemadji, and Montreal Rivers find their way to Lake Superior; the Menominee, Peshtigo, Oconto, Wolf, Sheboygan, and Milwaukee Rivers, together with numerous smaller waterways, are a part of the Lake Michigan system.
Wisconsin is bordered by more than five hundred miles of Lake Michigan and Lake Superior; the State Possesses close to 4,000 mapped interior lakes. To the northeast, chiefly in Vilas, Oneida, and Iron Counties, are the hundreds of small waters of the highland lake district. In the northwest, especially in Sawyer, Barron, Polk, Burnett, and Washburn Counties is a second group of small, closely set lakes. Eastern and southeastern Wisconsin have a generous number of moderatesized, scattered lakes. Lake St. Croix, an interruption the St. Croix River, and Lake Pepin, a widening of the flow of the Mississippi, are both long narrow bodies associated with hundreds of small flood plain lakes within the bottom lands that line these rivers. Of all Wisconsin lakes, Winnebago, in the Fox River Valley, is largest, covering 215 square miles.