Cineál Eoghain

The Cenél nEógain, or "kindred of Owen", are a branch of the Northern Uí Néill, who claim descent from Eógan mac Néill, son of Niall of the Nine Hostages. Originally their power-base was in Inishowen, with their capital at Ailech, in County Donegal. Under pressure from the Cenél Conaill they gradually spread their influence eastwards into modern counties Tyrone and Londonderry, pushing aside the Cruithin east of the River Bann, and encroaching on the Airgiallan tribes west of Lough Neagh. By the 11th century their power-base had moved from Ailech to Tullyhogue outside Cookstown, County Tyrone. By the 12th century the Cenél Conaill conquered Inishowen, however it mattered little to the Cenél nEóghain as they had established a powerful over-kingdom in the east that had become known as Tír Eoghain, or the "Land of Owen", preserved in the modern-day name of County Tyrone.

At their greatest they held land spanning much of County Tyrone, as well as parts of counties Londonderry, Donegal, Fermanagh, Monaghan, and Armagh.

Below is a list of their principle clans and septs.

The name O'Neill may come from Niall Glúndub, however the Clann Néill (more commonly known as Clan Neill) takes its name from his grandfather Néill Caille. The O'Neills and MacLaughlins who descend from this branch, were the two principal and most powerful septs of the Cenél nEógain, however the MacLaughlins defeat at the hands of the O'Neills in 1241 led to the O'Neills dominance over the Cenél nEógain.

The Clann Aodha Bhuidhe, or Clandeboye O'Neill, is a branch of Clann Néill, descended from Aodh Meth (Hugh the Fat), King of Ulster from 1196 to 1230; Aodh Medh's brother was Niall Ruadh (Red Niall), King of Ulster for a month after his death, and Prince of Tyrone. The eponym of the clan was Aodh Buidhe (Yellow Hugh) O'Neill (1260–83), grandson of Aodh Meth, and last King to be called King of Ailech; Aodh Buidhe was most notable for his close co-operation with the Earldom of Ulster. The Clandeboye O'Neills would later take control over most of eastern Ulster with the collapse of the Earldom of Ulster due to the invasion of Edward Bruce, whom they had opposed. Henry O'Neill of this line was King of Ulster from 1325 to 1344; Art O'Neill from 1509 to 1514.

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