Need a couple of counties to look at in western South Dakota for a diy mule deer hunt thanks in advance

Call up fish and game and ask to speak to a game biologist for that area.

I live in the area. Go northwest of Buffalo in Harding County. The very northwest corner of the state. Thousands of acres of public land and I know there are good numbers and some pretty big deer. You can almost hunt from Buffalo all the way to Montana. Best wishes.