I was born in Alabama and raised Texas, and I've always heard "y'all" used as second person plural. I think it's interested how English doesn't really have a standard for the second person plural and different regions have made up their own words for it, "ya'll" in the south, "yinz" in western PA, "youse" in the east. I'd be interested in hearing what the other English speaking regions of the globe use for this like in Australia, England, South Africa, etc.