I'm not in Ireland, nor am I sure if we're related, but your Thomas McGrail (b. 1835) is consistent with what I have on my earliest identified ancestor, Thomas, also in Co. Mayo ca. 1840. I haven't been able to pin the birthdate or parentage down exactly, though. Do you have a parish register or census that isn't readily available online?
Sorry to butt in uninvited, but any tips are most appreciated.