Even as far west as Colorado we used it the same way when I was young. Then I got a job at an NYC company and the gendered-ness of it was frowned upon. I actually switched to "ya'll" and it worked great. All the New Yorkers just thought that's how Coloradoans talk. So, thanks Texas.
Totally unrelated but this Blaze Foley song talks specifically about getting back to a place "where the people say ya'll." It's beautiful: