King George’s royal proclamation of 1763 established the “Indian Reserve” covering most of Ohio, Indiana, Illinois, Wisconsin, Michigan and Minnesota. European colonists were prohibited from trespassing - only a small number of British military outposts were allowed. Just a short time before the revolution, it got organized as part of Quebec.

Early in the revolution, it was taken by the colonists who declared it “Illinois County, Virginia” and allowed people to stream in and claim their homesteads (Note that the northern part was claimed by Connecticut as their own “Western Reserve”). Essentially all of southern Ohio, Indiana and Illinois was settled by people crossing the river from Kentucky, so it makes a lot of sense that you’d think that the southern parts of all these states seem more similar to each other than they are to their northern neighbors.

The next section north seems to have been mostly dominated by folks from the mid-Atlantic - Virginia, etc. And further north dominated by people that arrived on sailing ships, especially from New York. New Buffalo Michigan refers to Buffalo New York ;)

Anyway, it seems kind of weird that these states seem geographically oriented north-south but culturally oriented east-west. But the fact that they were depopulated (of Europeans) and then repopulated (by Europeans) gives an explanation of that, especially with the transportation available at the time of repopulation (of Europeans).