I'm surprised no one has brought it up so far. This is from way back when the US was still expanding east to west. Land Ordinance of 1785
It was literally just a means of dividing up the land to make it easier to manage. This is why much of the plains states follow such rectangular county/state lines between water geography.
Edit: States that had their counties/borders established before this act will have more organic geography following boundaries. Counties/States settled after 1785 will display this grid-like pattern.
Got any videos from these days? Always down for ska