These state names are a blend of Greek (Metropotamia, Chersonesus, Polypotamia, etc.) and Indian names. That 'sipi' ending means river (presumably in Algonquin). So all -sipi names are playing to local names. Assenesipia means 'Rock river.'

Place names are inherently stable, particularly names of rivers and mountains. A dramatic change of place name to something that is meaningful to newcomers but meaningless to locals is a common way of saying, 'This shit is ours now.' A blend of names says, 'We're in charge, but we're gonna try not to bother you, as long as you don't mess with us.' Alexander did a lot of that. He'd set up a loyalist Alexandria in every region (the Egyptian one being the most famous), but he'd try not to disrupt anything else. It helped keep the empire together, even if it pissed of a lot of his generals.

Jefferson is likely doing the same thing here. Sort of a 'This land is your land, this land is my land, but it's still more our land' kind of thing.