Not sure exactly where in the Great Lakes region OP is, but I can report that the Toronto area has a mix of grey, jet black, and dark brown squirrels. All three are the same species, just different phenotypes.

We have a variety of squirrels here. This one is part of the eastern gray squirrel species. We also have fox squirrels, American red squirrels, Northern flying squirrels, Eastern chipmunks, thirteen-lined ground squirrels, and woodchucks.