Couple of people have beaten me to the point, but

(a) I'm sure there were Cuaucasians/whites/whatever living in the Indian Nation. I think some of them had good reasons to be that far away from regulated society. They might have been just the people to be related to a cowboy who came to a sticky end.

(b) It was called the Indian Nation before the great Oklahoma land rush (1889?). How long before that, I don't know.