The Barony of Castlemaine was created in the Peerage of Ireland in 1812. The first Baron was also created a Viscount. The Viscountcy became extinct upon his death without children, but the barony passed, by a special remainder, to his brother Richard.

Barons Castlemaine (1812)

• William Handcock, 1st Viscount Castlemaine (1761-1839)
• Richard Handcock, 2nd Baron Castlemaine (1767_1840)
• Richard Handcock, 3rd Baron Castlemaine (1791_1869), elected a Representative Peer in 1841
• Richard Handcock, 4th Baron Castlemaine (1826_1892), elected a Representative Peer in 1874
• Albert Edward Handcock, 5th Baron Castlemaine (1863_1937), elected a Representative Peer in 1898
• Robert Arthur Handcock, 6th Baron Castlemaine (1864_1954)
• John Michael Schomberg Staveley Handcock, 7th Baron Castlemaine (1904-1973)
• Roland Thomas John Handcock, 8th Baron Castlemaine (b. 1943)