[paulmooreparks]

I grew up in the South, and I never encountered the use of "y'all" in a singular context (I'm 48). I'm not sure where that idea started.

Edit: I should instead say I never encountered it among actual locals using the word in normal speech. Later on, the plural was sometimes used jokingly after the idea that "y'all" was plural had taken hold in popular, non-Southern culture.