You are correct in your assumption, Terry. The reference you refer to is indeed that of the same Patrick Metcalf Halpin mentioned in a very old post of mine. After the Union in 1800 and the abolishment of the Irish legislature, P M Halpin, who had once served as Secretary to the Lord Chancellor, Lord Lifford, was out of a job and while he didn't exactly fall on hard times, was seriously out of pocket. He appealed for compensation, but was ultimately unsuccessful, and before he died (in about 1814, I think), he was regarded by the legal fraternity in Ireland as the Father of the Profession.
His half-brothers were the actor John Edmund Halpin, and the surgeon Oliver Halpin. Patrick had land in Wicklow too, and I think much of it was sold off for financial reasons. Louth was where the Halpins originally settled after moving to Ireland from England, either at the time of the Cromwellian atrocities, or much earlier. My hunch is they were Old English, and maintained contact with their relatives in England for many generations, before the link was finally broken for good late in the 18th century.