O'Brien


Select O'Brien Surname Genealogy

The O'Brien clan is the main family descended from Brian Boru, the legendary king of Ireland in the 10th century. The Ui Braians ruled over Munster after Brian Boru's death and later ranked as one of the chief dynastic families of Ireland. 

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Ireland.   The O'Briens continued to rule the kingdom of Munster until the land was divided in the 12th century and their territory became the kingdom of Thurmond (in present day Clare) instead.  Their ancestral home was Dromoland castle.  The O'Brien's rule would last until 1542 when Morrough O'Brien surrendered his sovereignity to the new kingdom of Ireland under Henry VIII. 

Over the subsequent centuries there were many O'Brien branches.  The Earls of Thurmond, representing the main descent, tended to be on the side of the English, the Viscounts Clare on the other hand being Catholic supporters were fighting in the French army.  A younger line produced William Smith O'Brien who with his family devoted themselves to the Irish cause at the time of the potato famine and led the Young Ireland Movement.  Other O'Briens of varying backgrounds also became engaged in the cause of Irish nationalism at this time.    

Under English pressure or prejudice, the "O" in O'Brien could disappear.  A third were registering as Brien instead at the turn of the century.  But O'Brien is back in fashion again.  Other name variants are Bryan, McBryan, O'Brian, O'Bryan, Bryant, and Breen.  

Elsewhere.  Today, due to the Irish emigration, there are almost four times as many O'Briens and variants outside Ireland than within, with the largest number being in America.

Select O'Brien Names

Brian Boru, the legendary 10th century Irish king, left his name to the O'Brien clan.
Murrough O'Brien, known as Murcha of the burnings, played a controversial role in mid 17th century Irish politics.  He was made President of Munster for expelling the Catholics and then became a Catholic himself.
William Smith O'Brien was the 19th century Irish nationalist who led the 1848 uprising after the potato famine.
William O'Brien was the Irish nationalist who founded the United Irish League, the forerunner to the nationalist Sinn Fein party.
Edna O'Brien is an Irish novelist and short story writer who novels were first banned in Ireland.
Aidan O'Brien is a very successful Irish horserace trainer.
Conan O'Brien is an American comedian and late-night talk show host.

Select O'Briens Today

  • 37,000 in the UK (most numerous in Lancashire)
  • 50,000 in America (most numerous in New York)
  • 108,000 elsewhere (most numerous in Ireland)
O'Brien is the #6 ranked surname in Ireland.


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For other surnames check the companion selectsurname.com site where there are to be found the history and genealogy for more than 500 surnames.

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