Found this site by chance, so here is what I know. Upon research G.C. McElfatrick, Sr., M.D. found that his McElfatrick ancestors are of Scotch-Irish descent and arrived in PA in the 1800s. There are currently McElfatricks in Baltimore, MD; Denver, CO; and Belfast,Ireland. There was also some indication that the McElfatrick name had some tie in with the McIlrath name. Good luck researching and happy hunting!