O’Brien Surname Genealogy

early history of the O’Brien
is as a Dalcassian tribe in SW Ireland and then with
Brian Boru, the legendary king
Ireland who defeated the Norsemen at Clondorf in 1014 but died in the
process. The Ui Braians ruled over
Munster after Brian Boru’s death and, as O’Briens, emerged as one of
dynastic families of Ireland.
Today, due to emigration, there are more O’Briens
outside Ireland than within, with the largest number being in America.There
are many name variants of O’Brien around the world, including Bryan,
McBryan, O’Brian, O’Bryan, Bryant, and Breen.

O’Brien Resources on

The Rock of
Cashel in Tipperary was the traditional seat of the Kingdom of Munster,
which the
O’Briens would hold until the 12th century.
After that time the territory was divided and they ruled over
kingdom of Thurmond in present-day Clare instead.

Their ancestral home in Thurmond was
Dromoland castle. The O’Brien’s rule would last until 1542 when
O’Brien surrendered its sovereignty to the new English kingdom of
Ireland under
Henry VIII.

Over the subsequent
centuries there were to be many O’Brien branches. The Earls of
representing the main descent, did tend to side with the English. Other O’Briens, although they had accepted
English titles, often ended up opposing the English cause:

  • Murrough
    O’Brien, the Earl of Inchiquin, having supported the
    English in 1641, switched sides and left Ireland for France and French
    service in 1650,
    his grandson was later to return in 1703.
  • while
    the Viscounts Clare left in 1690 and never returned.
    They raised the famous Irish brigade known as Clare’s
    and were fighting for France until the last of them
    died in

O’Briens at
Comeragh castle
in Waterford were almost wiped out
by Cromwell in 1656. After taking the
castle, he hanged four of the O’Brien brothers.
The fifth, John, managed to escape and from him came the
O’Briens of

The history of
the O’Brien clan
, up to the end of the 18th century, was
first compiled by John O’Donoghue in the book he published in 1860.

In the 19th century, from an
O’Brien Clare line, came William Smith O’Brien, an Irish nationalist
and one of
the leaders of the Young Ireland rebellion of 1848.
This led to his arrest, trial, and
transportation to Australia. Other
O’Briens of varying backgrounds were also to become engaged in the
cause of
Irish nationalism at this time.

Today in
Ireland, O’Briens are mainly found outside Dublin in the Munster
counties of
Clare, Limerick, and Cork.

America. A number of O’Briens came to
in the second half of the 18th century, including Morris
O’Brien who came to Machias in Maine. His son Captain Jeremiah
O’Brien was one of the early
American heroes
of the Revolutionary War. In 1775 he
captured a British armed schooner off Machias in the first naval
engagement of
the war. His son Jeremiah ran a
manufacturing and shipping business in Machias and was active in local

Born in Ireland in 1827, Hugh
O’Brien moved with his parents to Boston when he was five.
He prospered there as a printer. In
1885, he took the office of mayor of
Boston, the first Irish-born and the first Catholic to do so in a city
previously run by native-born Protestants.
A much later Boston celebrity is the talk-show host Conan
O’Brien who
grew up in a middle-class family in Brookline.
His forebears had immigrated to Boston from county Kerry at the
time of
the potato famine.

Canada. The
O’Brien name in various forms was evident in
Newfoundland by the late 18th century.
John O’Brien came to St. John’s around 1818.
A dairy farmer, he built Thimble Cottage in
the outskirts of the town. It still
stands, with the third generation of O’Briens living there.

O’Briens were also part of
the Irish community in Antigonish county, Nova Scotia.
The 1838 census listed O’Briens in Dorchester
and Tracadie townships. Richard Baptist
O”Brien, later a fervent advocate of Irish home rule, spent time as a
priest in
Antigonish county in the 1840’s. Michael
J. O’Brien, the railway industrialist, was born at Lochaber in 1851. He and his son Ambrose were influential in
the founding of the Montreal Canadiens and the National Hockey League.

O’Brien Miscellany

If you would like to read more, click on the miscellany page for
further stories and accounts:

Select O’Brien Names

Brian Boru,
the legendary 10th century Irish king, left his name to the O’Brien
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 Young Ireland uprising.  William
was the Irish nationalist who founded the United Irish
League, the forerunner of Sinn Fein.
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)
  • 60,000 in America (most numerous
    in New York)
  • 108,000 elsewhere (most numerous in Ireland)


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