Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
by 1879, U.S. dialect abbreviation of you all (see you).
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]
Online Etymology Dictionary, © 2010 Douglas Harper