According to local historian Fahey, the castle was built on an island where Guaire Aidne Mac Colmáin, a sixth century king of Connacht, had his palace. The O’Shaughnessy family made it their principal residence after Sir Roger O’Shaughnessy was created baronet by Henry VIII in 1545. The castle’s grandeur was legendary; in July of that year, O’Shaughnessy hosted the Lord Deputy at a banquet so lavish that witnesses claimed nothing like it had ever been seen in an Irish house before. By the mid-seventeenth century, a substantial dwelling house had been added near the castle, with the entire complex enclosed by a protective bawn.

The castle met its match in June 1650 when Parliamentary forces under Lieutenant-General Edmund Ludlow arrived to take possession. The defenders initially refused to surrender, claiming they’d already submitted to Sir Charles Coote and defiantly playing their bagpipes in contempt. Despite lacking artillery, Ludlow’s men launched a fierce assault, using fagots both as shields and to fill trenches or burn gates. The attackers scaled eleven-foot earthworks and twelve-foot walls whilst under heavy fire, eventually forcing their way through a barred stone window. The defence was led by Lieutenant Folliot, who fought desperately with a tuck in one hand and stiletto in the other before being run through. As fire spread through the structure, the remaining defenders, about eighty men plus women and children, finally surrendered. A Parliamentary diary records that forty rebels were killed in the storm, fourteen were shot afterwards, and the castle was burnt, though the house was preserved.

Following the Williamite War, the O’Shaughnessy family lost their ancestral seat when William O’Shaughnessy was declared attainted and fled to France; the lands were granted to Sir Thomas Preston in 1697. The final indignity came in the late eighteenth century when both the historic castle and mansion were demolished to make way for military barracks, their stones repurposed as building material. Today, only fragments remain: a twin-light late medieval window and what may be a medieval doorway, both incorporated into the later barrack walls, serving as the sole physical reminders of a castle that once hosted banquets fit for kings and withstood one of the most dramatic sieges of the Cromwellian conquest.