In Castlegar sat the Mahon family. The Mahons were settled at Castlegar from the late 17th century. They intermarried on a number of occasions with members of the Browne family of Westport. In 1819 the head of the family became a baronet. In the 1830s, at the time of the first Ordnance Survey, Ross Mahon was the proprietor of several townlands in the parish of Ahascragh. The Mahon estate was one of the principal lessors in the parish of Grange, barony of Loughrea at the time of Griffith's Valuation. Mr. Charles Filgate acted as agent for this property. The Mahons also held extensive lands in the baronies of Clonmacnowen and Killian. In the 1870s the Castlegar estate amounted to over 32 km2 (8,000 acres) in county Galway as well as over 3.2 km2 (800 acres) in the parish of Termonbarry, barony of Ballintober North, county Roscommon. In 1906 Sir William Mahon held over 4.9 km2 (1,200 acres) of untenanted land in the Ahascragh area. MacLochlainn writes that most of the estate was sold to the Land Commission in 1977.