The Kings of Ailech were the over-kings of the medieval Irish province of Ailech in north-western Ireland. It encompassed the territories of the Cenél nEógain and Cenél Conaill. After the battle of Cloítech in 789 its kings were exclusively from the Cenél nEógain. The royal fort for Ailech was the Grianan of Aileach, a hillfort on top of Greenan Mountain in modern-day County Donegal, Republic of Ireland.