I'd say in Dallas a bit more often but not really so much in Austin or downtown San Antonio. I mean you're going to see some but it's not like the "norm." It's so darned hot here most of the year, cowboy boots are not great in the heat unless you really need the foot protection out on the ranch. I live in the hill country and I do see cowboy boots (and hats) more often out here because people are "working their land" or walking on it a lot and want rattlesnake and rock protection for their feet.
All that said, they certainly are not out of place and there are some great stores to buy boots.
Are you coming to Texas?.....................