I generally find them in pastures that are grazed down a bit. Not a lawn, but far from a jungle...
And the tip about boots is a good one. Even when you get to know their habits in an area, you may still be doing a good bit of hiking before (or if) you find them.
If your dog is steady, I would not hack her back in at all. Let her run as far and wide as she wants to go. You're covering some big country going after early season chickens.
Bring plenty of water for you and the dog and pace yourself. It is still awfully damn hot and humid in September. I like to bounce along a creek if I am lucky enough to be hunting near one just to give the dog plenty of opportunities to dunk herself. I'm not really expecting to find chickens near the creek, but I'll just check back to it when the dog looks hot.
The young prairie chix might hold until you are nearly on top of them, but the old ones usually won't. They remember what's up, and will often start getting jumpy about the time you are walking into the edge of gun range. Sometimes there is a straggler even if the rest of the flock jumps early...
Good luck!