Two Supreme Court cases, Wisconsin v. Michigan, 295 U.S. 455 (1935) and Wisconsin v. Michigan, 297 U.S. 547 (1936), settled a territorial dispute between Wisconsin and Michigan.

Background

The 1836 boundary description between Wisconsin and Michigan described the line through northwest Lake Michigan as "the most usual ship channel". This description needed clarification as two routes were in use into Green Bay. Multiple islands lay in between and all were claimed as part of both Door County, Wisconsin, and Delta County, Michigan. A similar case, Michigan v. Wisconsin 270 U.S. 295 (1926), had previously been brought to the Supreme Court but was dismissed.

Decision

In 1936, the Supreme Court decision chose the ship channel through the Rock Island Passage as the more common, so Wisconsin retained the intervening water area with its islands: Plum, Detroit, Washington, Hog, and Rock.