Evolution of Michigan's Legal Boundaries
Few published maps show Michigan’s true boundary. Michigan’s legal boundary does not stop at the shoreline of the four Great Lakes that encircle it, but extends into them to include almost 40,000 square miles of water, comprising 40% of Michigan’s area. Most maps of Michigan show only the upper and lower peninsulas plus a few major islands. The U.S. Geological Survey recognizes 420 named islands in the Great Lakes belonging to Michigan.
Since statehood, eight challenges to the boundary have resulted in adjustments that relinquished territory to Minnesota, Wisconsin, and Ohio, but gained territory from Canada.
Sugar Island/St. George’s Island in the St. Mary’s River
The Webster-Ashburton Treaty, signed August 9, 1842, settled a border dispute with Great Britain in which Michigan gained governance over Sugar Island (called St. George’s Island by the Canadians).
The Minnesota Sliver
The Webster-Ashburton Treaty also settled the location of a point in Lake Superior that subsequently caused Michigan to relinquish a sliver of water to Minnesota.
The Toledo Strip
Part 1: The boundary with Ohio was hotly contested in the 1830s as a result of two surveys that left an areas of dispute amounting to 468 square miles on the Michigan-Ohio boundary. At the time of statehood, Michigan accepted the western portion of the Upper Peninsula instead of the "Toledo Strip".
Part 2: By 1914 survey markers had disappeared and the referenced "North Cape" of the Maumee river had eroded. To settle the new dispute peacefully, the line was re-surveyed and marked with sturdy granite pillars. Both sides agreed to accept whatever lines were agreed by landowners on both sides of the state line, resulting in a "sawtooth" shaped boundary.
The Wisconsin Wedge
A Supreme Court decision November 22, 1926 (Michigan v. Wisconsin 272 US 398) awarded a sliver of land to Wisconsin. The dispute arose because the original 1836 boundary description referenced a situation that didn’t exist: The referenced Montreal River did not originate from the Lake of the Desert.
Menominee River Islands
The islands of the Menominee River were divided in half by the US Supreme Court in 1926: Those north of "Quinnesec Falls" (now the site of Big Quinnesec Dam) were awarded to Michigan, and those south of the falls were awarded to Wisconsin.
When Is An Island Not An Island?
The U.S. Supreme Court declared in the case Michigan v. Wisconsin, decided November 22, 1926, that Merryman Island in Menominee County is "part of the mainland of Michigan."
The Green Bay Channel & Islands
The 1836 boundary description described the line through northwest Lake Michigan as “the most usual ship channel”. This description needed clarification as two routes were in use. The Supreme Court decision chose the northernmost ship channel, in which Michigan lost the intervening water area and four islands: Plum, Detroit, Washington, and Rock. The Michigan-Wisconsin boundary was finally settled and described in full March 16, 1936 in Wisconsin v Michigan 297 US 547.
The Lake Erie Triangle
The most recent dispute with Ohio brought into contention about 150 square miles of Lake Erie. Should the “northeast” line be a continuation of the gentle angle created by the Toledo Strip, or should upon reaching Lake Erie the line turn to a 45˚ angle? On February 22, 1973 the Supreme Court decided in favor of Ohio (Michigan v Ohio, 410 US 420).