Mayo is a maritime county in the province of Connacht and is bounded on the north and west by the Atlantic Ocean. Sligo and Roscommon border it on the east side and to the south lies county Galway.
Its greatest length, from a border point near Ballyhaunis to Erris Head, is 66 miles and its greatest breadth from Killary Harbour to Downpatrick Head is 54 miles.
According to the census returns of 2006, Castlebar in the centre of the county is the largest town in Mayo, (10,655) with Ballina, to the north following closely behind. (10,065) The former is the administrative seat of the county.
Ireland West International Airport is is located midway between Charlestown and the Marian centre of Knock.