I wonder if it possibly came down to you by water from Lake Huron to Lake Erie. Or was dropped along the path by some other Native American Tribes.
"drift copper" — removed from the rocks by the glaciers and dropped randomly in the glacial debris. The Indians were made aware of the existence of the metal by masses of float copper carried south by the glaciers and left lying on the surface.

Copper from these mines was widely distributed throughout the country, and it is probable that numerous tribes made summer pilgrimages to the Upper Peninsula to get supplies of the precious metal.
However it got there, it sounds like a really cool find