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The title ofBaron O'Brien has been created twice, once in thePeerage of Ireland and once in thePeerage of the United Kingdom.

The first creation was on 21 October 1654, whenMurrough O'Brien, 6th Baron Inchiquin, was created Baron O'Brien andEarl of Inchiquin. The barony and earldom became extinct on the death ofJames O'Brien, 3rd Marquess of Thomond on 3 July 1855.

The second creation was on 16 June 1900, whenSir Peter O'Brien was created Baron O'Brien. The title became extinct on his death on 7 September 1914.

• Baron O'Brien of Lothbury, life peerage created in 1973

• Noble titles created in 1654
• Extinct baronies in the Peerage of Ireland
• Noble titles created in 1900
• Extinct baronies in the Peerage of the United Kingdom

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