The castle’s origins date to 1628-33, when Robert Devereux, the third Earl of Essex, finally heeded advice to establish a stronghold in the barony of Farney, lands he had inherited at just twelve years old. Built approximately 800 metres west of what was likely the former power centre of Ever Mac Cooley Mac Mahon at Lough Lisanisk, the castle served as Essex’s occasional residence and the administrative heart of his Irish estates.

Thomas Raven’s 1634 survey reveals the castle as an impressive fortified house: a seven-bay, two-storey structure with three projecting wings housing staircases, all protected within a rectangular bawn featuring circular corner towers and a fortified gatehouse. The castle weathered the tumultuous events of the 1641 rebellion, when the earl’s agent Robert Branthwait was caught off guard but survived, and the subsequent siege and recapture by Crown forces. After passing through various aristocratic hands, including the Marquis of Hereford and later the Marquis of Bath, local tradition holds that Jacobite forces burnt the castle during the Williamite wars of 1688-9, leaving it in ruins by 1692.

The castle’s transformation came in 1851 when land agent William S. Trent rebuilt parts of the structure, likely constructing the castellated block that overlooks Castle Street today and incorporating the original corner towers and gatehouse into his design. The site took on its current religious character in 1888 when Father Peter Birmingham purchased the property for the Sisters of Saint Louis, who established a girls’ boarding school that continues to operate today, though now as a day school. Visitors can still spot elements of the original fortification in the convent building; the large bay windows at either end of the central block are thought to incorporate the bawn’s corner towers, whilst the castellated central section may be built around the original gatehouse.