Landed Estates
NUI Galway

Mahon (Castlegar)

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.


Name Townland Civil Parish PLU DED Barony County Map Ref
Ahascragh Glebe/Rectory Ahascragh West Ahascragh Ballinasloe Ahascragh 1 Kilconnell Galway OSI Ref: M780386
OS Sheet: 61
Discovery map: 47
Weston Weston Ahascragh Ballinasloe Ahascragh 1 Clonmacnowen Galway OSI Ref: M786396
OS Sheet: 61
Discovery map: 47
Ballyglass House Ballyglass (Mahon) Ahascragh Ballinasloe Killure 2 Clonmacnowen Galway OSI Ref: M811358
OS Sheet: 74
Discovery map: 47
Castlegar Castlegar East Ahascragh Ballinasloe Ahascragh 1 Killian Galway OSI Ref: M797 393
OS Sheet: 61
Discovery map: 47
Killareeny Killareeny Aughrim Ballinasloe Aughrim Kilconnell Galway OSI Ref: M748302
OS Sheet: 86
Discovery map: 47
Milverton Ahascragh West Ahascragh Ballinasloe Kilconnel Galway OSI Ref: M776386
OS Sheet: 61
Discovery map: 47

Archival sources

  • Pedigree of Mahon of Loughrea, Oughterclooney, Beech Hill and Castlegar, Co Galway and of Co Tipperary. GO MS 177: 438-451; National Library of Ireland
  • Pedigree of Mahon of Castlegar, c 1600-1818. GO MS 169: 250-251; National Library of Ireland
  • Draft trees and abstracts from parish and newspaper records of family of Mahon of Castlegar, 1656-1935. GO MS 813: 9; National Library of Ireland
  • Account of money expended on Eliza Robinson by Ross Mahon, Castlegar, her guardian, 1777-1785. MS 5004; National Library of Ireland
  • Copy of grant of arms to descendants of Ross Mahon, 9 Sept 1819. GO MS 106: 116; National Library of Ireland
  • Rentals of estates of the Mahon family at Castlegar, Co Galway & Termonbarry, Co Roscommon, 1841-1859, with some 20th century documents. MS 8553; National Library of Ireland
  • Mahon Papers, collection of estate and family records 1690-1957. Collection List 149, MSS 47,791-47,969 & MSS L 199-262; National Library of Ireland
  • Weston. Photographs. 022/096.; Irish Architectural Archive
  • Castlegar photos & press cuttings & a Christies sale catalogue. 0088/049 & D.CAS 4.0; Irish Architectural Archive
  • Mahon of Castlegar Papers, sketch plans of Castlegar House and plan of farmyard at Westport House, c 1800. MS 24,593; National Library of Ireland
  • Mahon Papers, mainly rentals, account books & diaries, 18th-19th centuries. MSS 9168-9172, MSS 19,963-19,999, MSS 23,001-23,047, MSS 23,344-23,474, MS 25,061.; National Library of Ireland
  • George C. Mahon Papers, mainly genealogical. MSS 22,190-22,245; National Library of Ireland
  • Guinness Mahon & Co Collection, includes conveyances of lands in Co Mayo in a chancery case Mahon v Mahon, 1862. Small Accs. Index 59, D.5884-5885; National Archives of Ireland
  • Catalogue for sale of contents of Castlegar House by Hamilton, Osborne & King & Christies, property of John Horan, 24 & 25 May 1988. SCRR; James Hardiman Library, National University of Ireland, Galway

Contemporary printed sources

Modern printed sources