I think I've figured it out. In "The Butt-head Experience," BH starts dreaming he's on-stage at a rock concert. It's hard to hear, but BH says to the crowd: "I hear Houston wants to party."
If B&BH didn't live near Houston, they would have never heard of the place. The only city they know of besides their hometown is Seattle, where "everybody you see is cool."
Of course, they don't actually live in Houston, but they probably live just north of it, somewhere is SE Texas. That would also explain the Southern accents that many of the characters have. ********** BH: "Some things just come natural. It's like taking a dump. When you're born, taking a dump just comes natural, but you have to learn how to take a dump in the toilet."
B: "You're pretty smart, Butt-head. I'm going to learn how to do that."
-- Son of Beavis