Hi Evelyn,
I think the Atlas is fairly accurate but a significant problem with Indian Territory is that places moved, particularly due to the railroads. Not only the towns that popped up on the railroads but the water stops would be named for something in their vicinity and would be shown on maps. The name of the water stop survives but not the location of the original site. (if that makes sense)

Another reason for the "moves" is the location of the post office. There were very few "towns" and the post offices were at a the postmaster's residence where everyone came to pick up their mail. If the postmaster changed then the post office location changed.

In the case of Hillabee, I think there were multiple places using that name. I think the location in the Atlas, as memory serves me, is the location G.W. Grayson is referring to on the northside of the Canadian about where Hanna OK is now. That location also fits with being 75 miles from Ft Gibson.

Ken