Prior to the Norman conquest of Ireland, the area was called Sliabh Lugha and was ruled by the Ó Gadhra dynasty. In the 12th century, Milo de Angelo removed the O'Gadhra seat from Airtech Mór to Costello. He built a castle there, known as Castlemore. The Ó Céirín (Kearns) family also had a presence as lords of Ciarraige Locha na nÁirne.
Name
The Costello family who gave their name to the Barony were originally Nangles, or de Angulos, who came to Connacht with the Anglo Normans in the 12th century. Gilbert de Angulo, Baron of Navan, arrived with his brothers who had been outlawed and expelled from their lands in Meath in 1195. They were later pardoned in 1206. In a number of grants to outlawed Norman lords at this time by Cathal Crobhdearg, King of Connacht, Gilbert and his brothers were given Máenmaige and Cairbre Drom Cliabh. The first reference to this family is in the Annals of the Four Masters in 1193. The sons of one of the first Nangles, Gilbert de Nangle, became known as the Oistealb, and gave rise to the surname Mac Oisdealbh, later MacOisdealbhaigh, anglicised to MacCostello. It was the first recorded instance of a Norman family assuming an Irish 'Mac' name. From that time forward, they became thoroughly Irish.[2] The family had focused their interests on grants in Breifne from 1221 until their expulsion in 1248 and after Gilbert's brother William de Angulo received the grant of Sliabh Lugha in the conquest of Connacht of Richard Mór de Burgh, 'Lord of Connacht' this focus shifted to the development of the Connacht holdings, now the Barony of Costello.
The MacCostello land was in the part of Mayo now known as the Barony of Costello until the end of the 16th century. In 1565, their seat of power was near Ballaghaderreen (now part of County Roscommon). Their name, although the Mac has now been dropped, is a common surname in both Mayo and County Galway where it is usually spelt with an extra 'e' at the end.
The Costello's were one of the many great Irish families[citation needed] which, during the seventeenth century destruction of everything Gaelic, produced famous rapparees who fought against Oliver Cromwell and the parliamentarians.
The local Costello landholders lost title to their lands to Theobald Dillon, 1st Viscount Dillon in some sharp practices during the period of the Tudor reconquest in the province of Connacht.[3] To save expense and ensure the smooth legal transfer he persuaded them to allow him surrender their lands for them in one land-title in the surrender and regrant process and have it regranted in his name, becoming the legal landowner in the process.[citation needed] He never returned the land-title to the native owners as had been intended. The title of Viscount Dillon of Costello-Gallen, was especially created for him in the Peerage of Ireland in 1622 when Lord President of Connaught confirming his position. This would lead to rapparee actions by Dudley (or Dubhaltach Caoch) Costello against the Dillons in the seventeenth century. Dudley was an officer in the army of the Confederate Catholics in 1642, and later became a colonel in the Spanish army. Returning to Ireland after the Restoration and disappointed by his failure to recover the family estates, he devoted the rest of his life to wreaking vengeance on the new Dillon proprietors until his death in 1667.
Loughglynn, built circa 1715, was the seat, or main residence, of the Dillon family in Costello who became absentee landlords in the nineteenth-century. The land remained with the Dillon family until Harold Dillon, 17th Viscount Dillon sold the estate in counties Mayo and Roscommon, amounting to 93,652 acres, to the Congested Districts' Board on 11 May 1899.[4]
By the terms of the County of Roscommon Act, 1840, two townlands of the parish of Kilcoman were detached from the barony of Costello in Mayo and transferred to the barony of Frenchpark in Roscommon. The townlands remained in the parish of Kilcolman.[11] The townlands moved to Frenchpark are Banada[12] and Keelbanada[13] The 1840 Act also transferred four townlands of the parish of Castlemore to the barony of Frenchpark: Aghalustia,[14] Cappagh,[15] Lissian[16] and Roosky[17] The four lay to the right bank or southern side of the River Lung, detached from the other townlands of the parish.
^McDonnell Garvey, Maire (2008). "The Barony of Costello 1585 – 1900"(PDF). The Corran Herald. No. 41. The Ballymote Heritage Group. pp. 29–30. Archived(PDF) from the original on 5 March 2019.
^Irish Statute Book - County of Roscommon Act, 1840 "And whereas the Townlands of Aughalusta, Lission, Cappagh, Roosky Banada, and Keel Banada, comprise a detached Portion of the County of Mayo in Ireland, being separated from that County by the River Lung, and are situated within the County of Roscommon, although not completely isolated therein; and it is expedient, for the Purpose of the General Survey of Ireland now carrying on under the Direction of the Master General and Board of Ordnance, and for the Purpose of the Valuation consequent upon such Survey, that such detached Portion of the County of Mayo should be comprised and included in the County of Roscommon, so that the said Counties of Mayo and Roscommon may respectively consist of One continuous Tract of Land:’ Be it therefore enacted by the Queen’s most Excellent Majesty, by and with the Advice and Consent of the Lords Spiritual and Temporal, and Commons, in this present Parliament assembled, and by the Authority of the same, That whenever the Surveyors or Persons appointed by the said Lord Lieutenant to ascertain and mark out the reputed Boundaries of each or any County, Barony, Half Barony, Parish, or other Division or Denomination of Land in Ireland, with a view to the more effectual Execution of the General Survey now in progress throughout Ireland under the Direction of Officers appointed by the Master General and Board of Ordnance, pursuant to the Provisions of an Act passed in the Sixth Year of the Reign of His Majesty King George the Fourth, intituled An Act to repeal an Act of the last Session of Parliament relative to the forming Tables of Manors, Parishes, and Townlands in Ireland, and to make Provision for ascertaining the Boundaries of the same, shall find that the said Townlands comprise a detached Portion of the County of Mayo, and that they are separated from the said County by the River Lung, and are locally situated within the County of Roscommon, although not completely isolated therein, the said Surveyors or Persons shall make a Report to the said Lord Lieutenant in Council, stating the Situation of such detached Portion of the County of Mayo and of the adjoining County of Roscommon, and describing the same in a Plan or Map to be annexed to such Report; and thereupon such Lord Lieutenant in Council shall make Order directing such detached Portion of the County of Mayo to be annexed to and incorporated with the County of Roscommon.."
