The advice we used to be given was to examine the registers of every parish within a 5 mile circle, then widen the circle, if still unsuccessful. Of course, if all of these parishes are on Ancestry, you have already done that, but it's worth checking. Are there no other Emmets in the neighbourhood at all? If there aren't, it certainly looks as though he came from somewhere else. Are there any marriage witnesses among the children of Thomas who might be relatives? Are there any Emmet wills in the neighbourhood? best wishes, claytonbradley