Y'all is spelled various ways:
Y'all
From Wikipedia, the free encyclopedia:
I usually spell it "y'all" (though I rarely write it) and I am from Tennessee. Texans who are up on their state history know that many early "Texicans" came from Tennessee (Houston, Crockett, etc.) and the vernacular is very similar. Several times when I traveled to New York, Boston or Philadelphia, locals have assumed I was from Texas or out west.
BTW, for those who don't know, many people use "y'all" as a singular pronoun (at odds with the Wikipedia entry); the plural is "all y'all".