Actually, English used to have a second person pronoun, thou/thy/thine/thee*. But that fell out of use, and you/your/yours/you became the norm.
For me, y’all is the second person plural, and declines as y’all/y’all’s/y’all’s/y’all.
*That’s subjective/possessive adjective/possessive pronoun/objective.
And y’all hail from? 
Uh…born in Durham, NC and lived there for three years, then moved to Columbus, OH for 14 years, then four years in Charlottesville, VA and almost three years in northern VA.
“Thou” isn’t any more plural than “you”. Actually, I think if anything it was less likely to be plural than “you”. The difference between “thou” and “you” was in the level of formality/intimacy.
To the OP: “Y’all” is plural. There may be a few small regions in Texas or the South where it is used in the singular, but I’ve never encountered anyone except damn Yankee using the word that way. “All y’all” can be used to clarify that each and every one of the people present is being addressed.
Oh, and I was born in Texas but we moved away before I was of speaking age!
Er, I meant to say that it was the singular pronoun. The formality bit mirrors what you see in French/Spanish.
Thanks.
Linguists at the University of Texas, San Antonia say that Texas are more likely to use ya’ll when addressing a single person.
I in an adjoining state also tend to use it for a single person.
hlanelee wins the prize for “you fuckers”.
I always use y’all as plural. I also use the possessive form of y’all’s pronounced more like “y’allez” as in “Is that y’all’s car?”
Born/raised in Alabama. Was made fun of for using y’all in Yankee South Florida. Free to use it without ridicule here in North Florida which is Southern.
2a. pa, ma, ne.
Anyway, I always use ‘y’all’ to speak of a group.
Meh? I have been known to damn things quite often, if that’s what you mean…
Grew up in Texas, moved away, still use ‘y’all’.
I hate to spoil the joke, but for those of you who are confused, carnivorousplant’s OP says “dammit” everytime s/he uses the word “y’all” in a sentence.
Question 2) with “y’all” is interrupted with a “dammit” and corrected to 2A), where it’s replaced by “you”.
Dammit.
There YOU go, I said “dammit” without saying “y’all”!
dammit.
2A) California
1)One always refers to a group. Sometimes it might be addressed to a single person, but in those cases it refers to a group, generally the person’s entire famdamily. “How are y’all?” is just shorthand for “How are you? How’s your spouse? The kids are doing fine, I hope. Your mother, I trust she’s keeping well?” If the questioner doesn’t know (or at least know of, we generally don’t have to have met people to ask after them) your family, “y’all” might refer to one’s roommates, friends, or other group that the questioner does know.
Re: people outside the Southeast thinking “y’all” sounds stupid. The way I look at it, if people are so closed-minded that they’re going to look down on someone for using a grammatically correct contraction, their opinion isn’t worth worrying about. And God help 'em if they don’t have equal scorn for people who say “youse,” which isn’t even a fucking word.
It’s the second person plural. That is its proper use. It can also be used as in CrazyCatLady’s example. There’s no need to say “all y’all;” that would be redundant.
Louisiana. Though I can and will use “standard English,” my speech gets more Louisiana in it every day. I’m not complaining, I’m just assimilating.
I’m a native Texan.
Y’all is nominally singular. When referring to a group, use All Y’all, as in
“Hey! All Y’all get yer butts over here!”
I think the best example is still, “Y’all been drinkin’. All y’all been drinkinn’.”
If I may digress, the response is often another confusion of plurality: “I had a couple”.
Y’all is plural.
After double checking my profile - I’m from Mississippi. 
Y’all is plural. Second person plural, to be precise. I don’t feel ashamed using it because it fills the second-person plural void in English, which is filled by an officially accepted pronoun in every other language I know.* Even English once had a second person plural (ye) which dropped out of use.
*Japanese, German, Albanian, French, and Spanish, if anybody cares. And nobody believes me when I swear that Spanish was harder than everything except Japanese but that’s a hijack for another thread.
It’s still plural in both usages. “Y’all been drinkin’” implies that not just the addressee, but others in his group have been drinking.
"All y’all been drinkin’ " would be used to indicate that every member of the addressee’s group has been drinking.
If it were only the addressee who’d been drinking, the statement would be “You(‘ve) been drinkin’.”