Castledermot Friary, Franciscan monastery ruins in County Kildare, Ireland

Castledermot Friary is a monastery site with church ruins in County Kildare, Ireland. The building features a single undivided nave, a chancel, a 14th-century side structure with three chapels along the eastern wall, and a tower for defense.

A monastery founded by Diarmait, son of Áed Róin, King of Ulster, stood here in the 9th century. The Franciscan friary was founded before 1247, with the first documented mention on 25 May 1247, when justiciar John fitz Geoffrey granted it 15 marks. Troops under Robert I of Scotland plundered and badly damaged the friary in February or March 1317; the town wall, built from 1295, spared the town itself. The friary was suppressed in 1540.

A carved tomb shows two figures in relief and bears an eight-pointed fleur-de-lys cross, a symbol rarely seen in this form. This burial monument speaks to the importance of the individuals and their place in the community during the medieval period.

The ruins sit on the western side of Route R448 at the southern edge of Castledermot and are visible from the road. Access is straightforward, giving visitors a clear view of the remaining walls, chapels, and the defensive tower.

The monastery is one of only three Franciscan churches in Ireland with a northern transept featuring three pointed arches. This architectural feature makes it notably rare among similar sites across the country.