Today No One Knows the True Border Between Michigan and Ohio
The border between Michigan and Ohio has been one of the most controversial and fought over in American history. Of course you've heard of the Toledo War where the State of Ohio and Michigan Territory nearly came to armed conflict. Centuries later the border was still being contested as recent as a 1973 Supreme Court case.
Why is the border between these two states so contentious. Believe it or not, it's because the basis for the border line is now lost.
A fascinating article in the Fall 2018 Michigan Historical Review called "A Long Overdue Evaluation" by surveyor and historical Jack Owens tells the long story of the Michigan-Ohio border. The key reason for the conflict is the point that is to mark the beginning of the border, the "Southerly Point of the North Case of Maumee Bay" doesn't exist anymore. Owens writes,
the waves and weather of Lake Erie [have] erased all trace of the southerly half mile of the North Cape, and the last granite boundary post (No. 71) of that resurvey has to be set more than a mile and a half to the west on the closest terra firma.
The 1973 Supreme Court ruling that finally set the border also created the geographic oddity of Turtle Island, a small uninhabited dot of land in Lake Erie that is divided between the two states.