[1] The sept of Uí Briúin he belonged to was the Síl Cellaig of Loch Cime (Lough Hackett, near Headford in modern County Galway) named for his father.
[2] Also in 743 the Ui Aillelo fought a battle in Mag Luirg (Moylurg, the plains of Boyle) with the Gailenga.
[3] Fergus himself had to impose his authority and in 746 in alliance with the Conmaicne he was defeated by opponents from the Uí Briúin.
[7] The Ui Briun expansion to the north met with the hostility of the Cenél Coirpri branch of the Uí Néill.
Three of his sons Catharnach, Cathmug, and Artbran were slain in 758 at the Battle of Druim Robaig (Dromrovay, southern modern County Mayo) by the Uí Fiachrach in 758.