I'm not saying it's exclusively south, it's just more common to hear y'all in a southerner's vocabulary. Some other places might just say "you" or use more than one word "you guys" "all you/you all" etc... I don't use "ain't" either as it's not a real word, it's just mainly heard in slang and "ebonic dialects."
A lot of Slavic languages have this form as singular-formal form. In Slovak: Vy, in Russian, Ukrainian (and i guess also Serbian) ви. We used to use "Wy" in Polish, but it is archaic now. You can sometimes find it in films about military.