The Northern Uí Néill is the name given to several dynasties in north-western medieval Ireland that claimed descent from a common ancestor, Niall of the Nine Hostages. Other dynasties in central and eastern Ireland who also claimed descent from Niall were termed the Southern Uí Néill (together they are known as the Uí Néill dynasty). The dynasties of the Northern Uí Néill were the Cenél Conaill and Cenél nEógain, named after supposed sons of Niall: Conall and Eógain.

The Northern Uí Néill's over-kingdom in its earliest days was known as In Fochla and In Tuaiscert, both meaning "the North", and was initially ruled by the Cenél Conaill. After the Cenél nEógain's rise to dominance, it became known as Ailech.

Mythical origins

It is claimed in medieval Irish texts that around 425, three sons of Niall Noígiallach—Eoghan, Conal Gulban, and Enda—along with Erc, a son of Colla Uais, and his grandchildren, invaded north-western Ulster. The result was the vast reduction in the territory of the Ulaid, with the portion of land taken by the three sons of Niall becoming the kingdom of Ailech. This land was divided between the three brothers as such: Conal Gulban took the western portion and named it Tír Chonaill; Eoghan took possession of the main peninsula and named it Inis Eoghain; Enda took nominal possession of land lying south of Ailech, which became known as Magh Enda.