County Mayo is a county in Ireland. It is located in the West Region, and it is also part of the provinceof Connacht. It is named after the village of Mayo, which is now generally known as Mayo Abbey. Mayo County Council is the local authority for the county. The population of the county is 130,638 according to the 2011 census. The boundaries of the county, which was formed in 1585, reflect the Mac William Íochtar lordship at that time.

It is bounded on the north and west by the Atlantic Ocean; the south is adjacent to County Galway, the east is adjacent to County Roscommon; the northeast is adjacent to County Sligo. Mayo is the third-largest of Ireland’s 32 counties in area and 15th largest in terms of population. It is the second-largest of Connacht’s five counties in both size and population. There is a distinct geological difference between the north and the south of the county. The north consists largely of poor subsoils and is covered with large areas of extensive Atlantic blanket bog, whereas the south is largely a limestone landscape. Agricultural land is therefore more productive in the south than in the north.