"you people, you-all," contracted from U.S. dialectal you-uns, for you-ones (see you, also see y'all); first noted 1810 in Ohio. Also yinz; now considered a localism in Pittsburgh, Pa.
Entries linking to yins
you pron.
Old English eow, dative and accusative plural of þu (see thou), objective case of ge, "ye" (see ye), from Proto-Germanic *juz-, *iwwiz (source also of Old Norse yor, Old Saxon iu, Old Frisian iuwe, Middle Dutch, Dutch u, Old High German iu, iuwih, German euch), from PIE *yu, second person (plural) pronoun.
Pronunciation of you and the nominative form ye gradually merged from 14c.; the distinction between them passed out of general usage by 1600. Widespread use of French in England after 12c. gave English you the same association as French vous, and it began to drive out singular nominative thou, originally as a sign of respect (similar to the "royal we") when addressing superiors, then equals and strangers, and ultimately (by c. 1575) becoming the general form of address. Through 13c. English also retained a dual pronoun ink "you two; your two selves; each other."
y'all pron.
by 1879, U.S. dialect abbreviation of you all (see you, and compare yins).
Children learn from the slaves some odd phrases ... as ... will you all do this? for, will one of you do this? ["Arthur Singleton" (Henry C. Knight), "Letters from the South and West," 1824]
We-all for "us" is attested by 1865; we-uns by 1864. Who-all attested from 1899.