TitleDate of creationSurnameCurrent statusNotesO'Brien of Ardtona1916O'Brienextinct 1916first Baronet created Baron Shandon in 1918O'Brien of Kilfenora1891O'Brienextinct 1914first Baronet created Baron O'Brien in 1900O'Brien of Merrion Square and Borris-in-Ossory1849O'BriendormantLord Mayor of Dublin; sixth Baronet died 1982O'Loghlen of Drumcanora1838O'LoghlenextantO'Malley of Rosehill1804O'Malleyextinct 1892O'Connell of Lakeview1869O'ConnellextantO'Neill of Cleggan1929O'Neillextantfirst Baronet created Baron Rathcavan in 1953Oakes of Hereford1815Oakesextinct 1927first Baronet had already been created a Baronet in 1813, which creation became extinct in 1822Oakes of Nassau1939OakesextantOakes of the Army 1813Oakesextinct 1822first Baronet obtained a new patent in 1815, which creation became extinct in 1927Oakshott1959Oakshottextantfirst Baronet created a life peer as Baron Oakshott in 1964, which title became extinct in 1975Ochterlony of Ochterlony1823Ochterlonyextinct 1964had already been created Baronet of Pitforthy in 1816, which title became extinct in 1825Ochterlony of Pitforthy1816Ochterlonyextinct 1825also created Baronet of Ochterlony in 1823, which title became extinct in 1964Ogle of Worthy1816Ogleextinct 1940Ohlson of Scarborough1920OhlsonextantOppenheimer of Stoke Poges1921Oppenheimerextinct 2020Ormsby of Cloghans1812Ormsbyextinct 1833Orr-Ewing of Ballikinran1886Orr-EwingextantOrr-Ewing of Hendon1963Orr-Ewingextantfirst Baronet created a life peer as Baron Orr-Ewing in 1971, which title became extinct in 1999Orr-Lewis of Whitewebbs Park1920Orr-Lewisextinct 1980Osler of Norham Gardens1911Oslerextinct 1919Otway of Brighthelmstone1831Otwayextinct 1912Ouseley of Claremont1808Ouseleyextinct 1889Outram of The Bengal1858OutramextantOwen of Orielton1813Owenextinct 2002
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