Great that you got Thomas's death cert. What age was he? Who was the informant - any relation? What was his address as per death cert? You should be able to find Thomas on at least one of the censuses (assuming he was born pre-1901/1911).
Was he married? If so, do you know to whom, and when? If you can get a marriage cert, that will give his father's name.
If you know who his father was, you may be able to get more info on his family, and possibly discover if, in fact, the Patrick Conlon who died in America was an uncle of Thomas's.
Happy hunting!