Originally known as Aidhne, it was said to have been settled by the mythical Fir Bolg. Dubhaltach Mac Fhirbhisigh's Leabhar na nGenealach states that the Tuath mhac nUmhoir were led by leader Conall Caol, son of Aonghus mac Úmhór. Connall was killed at the Battle of Maigh Mucruimhe in 195, and his body brought back to Aidhne where it was interred at a leacht called Carn Connell (itself the site of a major battle some centuries later).
Located in the south of what is now County Galway, Aidhne was coextensive with the present diocese of Kilmacduagh. It was bounded on the west by Loch Lurgain (Galway Bay) and the district of Burren in County Clare. County Clare also bounds Aidhne on its south and south-east side. Aidhne is bounded on the east by the low mountains of Slieve Aughty, which separated Uí Fhiachrach Aidhne from Uí Maine.
On the north-east Aidhne is bounded by the plains of Uí Mhaine and on the north by Maigh Mucruimhe (the area around Athenry). On the north-west it was bounded by the parish of Maree which was in the territory of Uí Bhriúin Seola.
The diocese of Kilmacduagh contains the civil parishes of Kinvarradoorus, Killinny, Killeenavarra, Drumacoo, Kilcolgan, Ardrahan, Stradbally, Killeeneen, Killeely, Killora, Killogilleen, Kilchreest, Isertkelly, Killinan, Kilthomas, Kilbeacanty, Beagh, Kilmacduagh, Kiltartan.