Thanks for your message. My 3rd Great Grandfather's name was a George Petty as well. He is listed as living in Ballisnahyny, County Mayo on the marriage record of my 2nd Great Grandfather, William Petty.
By any chance, do you have the actual marriage certificate of Dominic Petty? If so, it should state their residence at the time of the marriage. It should also list the names of witnesses which sometimes can be siblings.
I look forward to hearing from you.