There were numerous John Keanes and birth, death, marriage & immigration records start to get more sparse pre-1851. That's a real problem. I was stuck at a similar point and made the biggest breakthough by doing a Y-DNA test through the Cain DNA project at www.familytreedna.com/public/Cain-Caine
Seems my surname can be Cain/Caine/Kain/Kane/Keane but fortunately the DNA mutates less than the surname. It's now clear from my Y-DNA matches that my clan were from Co Galway, but there were several unrelated Irish clans named O'Cathain. Fortunately their Y-DNA footprints tend to point to their original clan area in whatever part of Ireland they originated.