William A. McWilliams, was a son of Andrew J. & A. (Osborn) McWilliams. His siblings were: James Isaac McWilliams John T. McWilliams Jane McWilliams Lydia A. McWilliams Hooks Sarah P. McWilliams Smith Susan C. McWilliams Burley Benjamin F. McWilliams Martha Ella McWilliams Baker Andrew McWilliams Louis McWilliams He also had 3 half-siblings: Lou Della McWilliams Giles Robinson Stout, Alice McWilliams Giles and Calvin W. McWilliams.
He married Mary Frances Ferguson on Dec 23, 1875 in White Co., AR and they had 2 sons, John T. and Hubard who died young. After Mary died, he married Eugenia Elizabeth "Lizzie" Blackwell on Dec 7, 1884, in White Co., AR.