I’m not sure of the exact boundaries of “Hill Country” either. I spent a couple weeks at Davis Mountain State Park awhile back. It’s near the Ft Davis Historical Site. The name escapes me but there’s an observatory down the road also. Marta is nearby. It’s sort of an artsy hippie settlement that’s worth exploring. Lots of free roaming wildlife in the park.
If you travel with a dog, mine strongly recommends the ice cream parlor across from Ft Davis. They have a Milkbone & 1/2 scoop ice cream sundae just for dogs.
One heads up. It’s in a signal black hole. No cellular or OTA TV.