Iar Chonnachta (English spelling- Iar Connacht) covers the portion of County Galway west of Loch Orbsen (Loch Corrib) and the Gaillimh (the Galway River- better known as the River Corrib) and the portion of County Mayo in the barony of Ross. Iar Chonnachta means "West Connacht", or "west of Connacht", indicating that it was once perhaps considered to be beyond Connacht - or the lands of the Connachta - proper.

The territory of Dealbhna Thíre Dhá Locha / Delbhna Tir Dha Locha covered the eastern half of Iar Chonnachta. Connemara / Conmhaicne Mara (Conmaicne Mara) covered the western portion of the territory. Joyce Country (the Barony of Ross) covered the north-eastern portion of Iar Chonnachta. The native rulers of Joyce Country were the Partraighe an tSléibhe whose territory also covered the south of the barony of Carra in County Mayo.

Maigh Seola the plain lying on eastern side of Loch Corrib was up to the 1220's ruled by the O Flahertys. However, they were exiled into Iar Connacht by the O Connor Kings of Connacht, and their remaining land east of the river at Dun Beal Gallimhe was seized by Richard de Burgh in the 1230's. The O Flahertys seized control of Delbhna Tir Dha Locha and Conmaicne Mara from its ruling dynastys, and remained as lords of Iar Chonnachta for a number of centuries until they lost their lands in the upheavals of the mid 1600's.