- In the 1660s Sir James Shaen of Kilmore, county Roscommon, Surveyor General of Ireland, bought a large portion of the barony of Erris, county Mayo, from Robert Viner, a London goldsmith, who had been granted the lands by Charles II in payment of a debt. In 1695 the estate of approximately 95,000 acres was inherited by Sir James' son Arthur and subsequently passed to the Bingham and Carter families through marriage with the two daughters and heiresses of Sir Arthur. Sir Arthur granted leases in perpetuity to the Protestant settlers he introduced onto his estate.
- The Mahons were settled at Castlegar from the early 18th century. In 1711 the Earl of Clanricarde leased Castlegar to Bryan Mahon for lives renewable for ever. 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 8000 acres in county Galway as well as over 800 acres in the parish of Termonbarry, barony of Ballintober North, county Roscommon dated 1708. The county Roscommon estate was held on a lease for lives renewable for ever from Sir Arthur Shaen of Kilmore, county Roscommon. In 1906 Sir William Mahon held over 1200 acres of untenanted land in the Ahascragh area. MacLochlainn writes that most of the estate was sold to the Land Commission in 1977. The Mahon Papers, which document their estates in counties Galway and Roscommon, are available for consultation in the National Library of Ireland, Kildare Street, Dublin.