Iar Chonnachta (longer form - Iarthar Chonnachta) (alternative spelling- Iar Chonnacht) covers the portion of County Galway west of Loch nOirbsean (Loch Corrib) and the Gaillimh / Galway River (better known as the River Corrib) and the portion of County Mayo in the barony of Ross. Iar Chonnachta means "West Connacht". They area of Co. Galway lying between Kilkieran Bay to the west and Loch Corrib to the east is sometimes described as Iar Chonnnacht on maps and in books however this is incorrect as this area was the territory of Dealbhna Thíre Dhá Locha which only ever formed a part of Iar Chonnacht.

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. Dealbhne Thíre Dhá Loch(a) (The Dealbhne of the Two Lochs) was a tuath (a tribal kingdom) of medieval Ireland, located in Iar Connacht in the west of Co. ... The Conmaicne or Conmhaicne (descendants of Con Mhac) were an ancient tribal grouping that were divided into a number of distinct branches that were found scattered around Ireland in the early medieval period. ...

Maigh Seola the plain lying on eastern side of Loch Corrib was also considered to be part of Iar Chonnachta up until the 1200s when the native rulers of Maigh Seola - the O Flahertys who styled themselves the lords of Iar Chonnachta were ousted from Maigh Seola during the Anglo-Norman invasion of Connacht in that century. As they were the most powerfull clan in this part of Connacht it seems reasonable that the O Flahertys and the earlier kings of Maigh Seola were styled the kings or lords of Iar Chonnacht. The O Flahertys fled into what is now considered Iar Chonnachta and established themselves over the native ruling dynastys although the O Flahertys are believed to have had already had control over the Dealbhne Thíre Dhá Locha. The O Flahertys remained as lords of Iar Chonnachta for a number of centuries until they lost their lands in the upheavals of the mid 1600's. Maigh Seola was a term used to describe the land along the east shore of Lough Corrib, bounded by the river Clare which formed the border with the Hy-Many vassel kingdom of Soghain. ...