Baron Castletown, of Upper Ossory in the Queen's County, was a title in the Peerage of the United Kingdom. It was created on 10 December 1869 for John FitzPatrick, the former Liberal Member of Parliament for Queen's County. He was the illegitimate son of John FitzPatrick, 2nd Earl of Upper Ossory. The barony became extinct upon the death of his son, the 2nd Baron, on 29 May 1937.
Barons Castletown (1869)
- John Wilson FitzPatrick, 1st Baron Castletown (1811–1883)
- Bernard Edward Barnaby FitzPatrick, 2nd Baron Castletown (1849–1937)