The O’Neill family history can be traced back to 360 AD. They are descended from the royal family of Tara, who were kings of Ulster and monarchs of all Ireland from the 5th to the early 17th centuries. The surname comes Niall Glúin Dubh (Niall of the black knee), who was King of Ireland from 890 until he was slain in 919. The first recorded spelling of the family name is shown to be that of Donell O’Neill, grandson of Niall Glúin Dubh, dated c1000, in the ‘Historic Annals of Ireland’, during the reign of King Malachy 11, known as ‘High King of Ireland’, 977 – 1002. In addition to the O’Neills of Ulster, where the family is most numerous, there were sets in Thomond (counties Clare and Limerick), Decies (Waterford), and County Carlow.
The legendary Niall of the Nine Hostages was also a remote ancestor. He established himself as King of Midhe (Meath) at Tara around 400 AD. His kingship was followed by many of his descendants, thereafter referred to as the Ui Neill. The Ui Neill dynasty divided into two in the 400’s, the Northern Ui Neill (Cineal Eoghain and the Cineal Conaill) remained in the north while the Southern Ui Neill moved to Meath and the eastern midlands – they took it in turns to be Kings of Tara and, later, High Kings of Ireland.
In Griffiths Valuation c1850s, the Neills numbered 2578 households, while the O’Neills had 2720 households – a fairly even distribution. More than half of the O’Neills (1412), and one fifth of the Neills (537), were in the six counties that now make up Northern Ireland.