Ibar macRiangabra: Conchobar's charioteer
Id macRiangabra: Ferdiad's charioteer, brother to Laeg
Ilgarech: a hill near Garech, q.v.
Iliach: grandfather to Conall Cernach
Illann Ilarchless: an Ulster warrior, son to Fergus
Imchad: son to Fiachna
Imchlar: near Donaghmore, west of Dungannon, in the County Tyrone
Immail: a place in the Mourne Mountains, in Ulster
Imrinn: a druid, son to Cathba
Inis Cuscraid: Inch, near Downpatrick