The most prominent sept is that of the Connacht O'Connors who gave us the last two High-Kings of Ireland: Turlough O'Connor (1088-1156) and Roderick O'Connor (1116-1198). They trace their heritage and name from the Irish "Ua Conchobhair," meaning from Conchobhar, a king of Connacht.
9. O'Neill – from a champion, Niall of the Nine Hostages
The O'Neill family traces its history back to 360 A.D. to the legendary warrior king of Ireland, Niall of the Nine Hostages, who is said to have been responsible for bringing St. Patrick to Ireland.
Niall is also said to have been incredibly fertile – he has 3 million descendents worldwide.
“O’Neill” is derived from two separate Gaelic words, "Ua Niall," which means grandson of Niall, and "Neill" meaning "champion."
Ireland’s O'Neills were known by the nickname "Creagh," which comes from the Gaelic word "craobh" meaning branch, because they were known to camouflage themselves to resemble the forest when fighting the Norsemen. Crafty fellows, those O’Neills.
10. O'Reilly - ?
The O'Reillys round out the top 10 most popular names in Ireland.
Their family name is derived from the Gaelic "O'Raghailligh," meaning descendants of Raghaillach.
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.
Reilly, often spelled Riley, has become a trendy given name in the U.S., for both baby boys and girls.
Originally published in 2010.