The building that sits on a low ridge between Lough Rinn to the west and Lough Errew to the east is a Tudor-Revival country house built in 1833, its castellated associations borrowed from architectural fashion rather than military history. The name gestures at something ancient, but the oldest structure recorded on the site before the house went up was, according to an eighteenth-century survey map, an 'old stable'.

The family behind the house came to prominence through a combination of strategic marriage and well-placed connections. Nathaniel Clements, born in 1705, was not among the original planters who settled County Leitrim in the 1620s; his route into the county came later and by different means. A family connection to the Irish Treasury, and his 1730 marriage to Hannah Gore, a niece of Sir Ralph Gore who served as Speaker of the Irish House of Commons from 1729 to 1733, opened considerable doors. Over the following decades Nathaniel assembled a remarkable portfolio of land: Lord Boyne's Donegal estate in the 1740s, the Mohill estate of the Croftons in 1749, the Glenboy estate in north Leitrim in 1754, and then the estate and town of Manorhamilton in 1759, which made him the largest single landholder in the county. By 1760 he is recorded as holding some 85,000 acres across Donegal, Leitrim and Cavan, with a rental income of £6,000 a year. He commissioned a survey of the Lough Rinn lands from William Wogan in 1750, possibly with the intention of building there, but no house followed during his lifetime. It was his son Robert who became the first Earl of Leitrim in 1795, and it was a later Robert, Viscount Clements, for whom the present house was built in 1833, probably to a design by the Scottish architect William Burn. An east wing was added in 1889 to designs by Sir Thomas Drew for Colonel H. T. Clements, giving the building its current form. The house operates today as a hotel.