Everything you need to know about the Irish surname O'Reilly - its meaning, origins, interesting facts, and famous people with the last name O'Reilly.

Irish derivation of O'Reilly:

Ó Raghallaigh.

Name meaning of O'Reilly:

"Descendant of Reilly (extroverted one)."

Counties associated with the name O'Reilly:

Cavan, Longford, Meath, Westmeath, Fermanagh, and Monaghan.

O'Reilly coat of arms motto:

"With fortitude and prudence."

Looking for more on your Irish surname? Visit our Irish clans and surnames page here. 

History of the Irish surname O'Reilly:

The surname O'Reilly originates in County Cavan. The O'Reilly's were known as the Princes of East Breffny, descended from Raghallaigh, Prince of Breffny in 981.

They maintained their territory during the Anglo / Norman invasion of Strongbow, Earl of Pembroke, in 1172, but Sir John O'Reilly, Prince of Breffny surrendered the principality to Queen Elizabeth I thereby ensuring that his territories remained intact.

Interesting facts about the Irish family name O'Reilly:

 - Increasingly becoming a popular first name in the US.

- The O'Reillys were the most powerful sept of the old Gaelic kingdom of Breffny (Cavan and the surrounding counties), and the family is still prominent in the area.

Some famous O'Reillys:

- Bill O'Reilly (b.1949, American commentator and television show host of "The O'Reilly Factor" on the Fox News Channel

- John O'Reilly (Leader of The Saint Patrick's Battalion of Mexico)

- Sidney Reilly (1874–1925, Russian-British spy)

- Tony O'Reilly (b.1936, Irish billionaire businessman)

Looking for more on your Irish surname? Visit our Irish clans and surnames page here. 

Are you an O'Reilly? Done some family research on your name? Let us know what you've found, or just say hello to your fellow O'Reillys, in the comments section, below. 

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* Originally published in Aug 2016, updated in 2022.