A branch of the O'Conor Don family who resided at Dundermot for 2 generations in the 19th century. In 1683 Hugh O'Connor was granted over 1,800 acres in county Roscommon, including the castle of Ballyntobber and lands at Laraha and Ross. At the time of Griffith's Valuation, Patrick O'Conor held land in the parishes of Kilcroan and Kilbegnet, barony of Ballymoe, county Galway, and in the parishes of Oran and Drumatemple, barony of Ballymoe, Lissonuffy, barony of Roscommon, county Roscommon. Some of this land was held from the Blakeneys and some of the land in the parish of Oran was offered for sale by the Brownes of Castlemagarrett, county Mayo in May 1852. His brother Roderic also held land in the parishes of Oran and Drumatemple. In 1851 some of Roderick O'Connor's land in the parish of Drumatemple was advertised for sale in the Encumbered Estates' Court by his assignee Christopher Hume Lawder. From 1853 Patrick O'Conor held Laragh and Ross, which adjoined the demesne of Dundermot, from Arthur Irwin Mahon. Mahon advertised these lands for sale in May 1856. Patrick O'Connor and Charles O'Connor also held extensive lands at Rathconor and Tonlegee, parish of Kilbride, barony of Ballintober South at the time of Griffith's Valuation, previously part of the Croghan estate. In the 1870s Hussey records that the late Patrick Hugh O'Conor of Dundermot owned 2,435 acres in county Roscommon and his brother Nicholas O'Conor owned 810 acres. Nicholas O'Conor, a prominent British diplomat, sold Dundermot. The estate of his daughter Fearga O'Conor was vested in the Congested Districts' Board in March 1915.