The site likely dates to between 1182 and 1187, when the powerful Anglo-Norman lord Hugh de Lacy constructed it atop an earlier Irish fortress known as Rath Guaire. This layering of history, with Norman fortifications built over native Irish strongholds, was a common pattern during the medieval conquest of Ireland.

The castle’s ownership tells a story of shifting allegiances and power throughout the medieval period. Initially granted by Hugh de Lacy to his kinsman Sir Robert de Lacy, the territory of Killucan changed hands several times over the centuries. During Edward I’s reign (1272-1307), the lands passed to Mortimer, Earl of March, before eventually being granted to Sir John D’Arcy, Chief Governor of Ireland, during the reign of Edward III (1327-77). These transfers reflect the complex politics of medieval Ireland, where loyalty to the English crown was rewarded with substantial land grants.

While the original timber structures of the motte and bailey have long vanished, tantalising remnants of the site’s later development remain. The 1837 Ordnance Survey map shows a stone castle standing just south of the motte, and fragments of what may be 13th-century masonry can still be spotted in the motte’s defensive ditch. These stone ruins likely represent a later medieval upgrade to the original earthwork fortifications; a common evolution as temporary campaign castles became permanent centres of Norman control. Though the stone castle’s foundations are no longer visible, the earthen bank and external fosse that once enclosed the bailey still hint at the formidable defences that once protected this strategic stronghold.