Óengus mac Mugróin (died 803) was a king of the Uí Failge, a Laigin people of County Offaly.
[2] A conflict within the Uí Failge led to a slaughter in 789 at Cluain Ferta Mongáin (Kilclonfert, County Offaly) by Óengus at which his cousin Áed mac Tomaltaig was slain (their fathers were brothers).
[3] In 803 he was treacherously killed by the followers of Fínsnechta Cethardec mac Cellaig (died 808), over king of Leinster.
[4] Finsnechta was ensuring his control of the church of Kildare which led to conflict with the Uí Failge.
His grandson Máel Sinchill mac Mugróin (died 881) was a King of the Uí Failge.