The site consists of a substantial walled courtyard, roughly square in shape and measuring approximately 30 by 40 metres, with the ruins of a tower house positioned at its northwest corner. When the Ordnance Survey documented the castle in 1840, they found the north wall of the tower still standing at about 9 metres high, its 1.4 metre thick walls testament to the defensive requirements of medieval Ireland. The bawn walls, though partially ruined, still reached heights of up to 5 metres in places, with stone steps at the northeast corner that once provided access to the wall walk where sentries would have kept watch over the surrounding countryside.

The castle’s history reveals the changing fortunes of Anglo-Irish nobility throughout the turbulent 16th and 17th centuries. Originally a manor belonging to the powerful Earls of Kildare, Rathcannon passed into Crown hands following the rebellion and execution of ‘Silken Thomas’ Fitzgerald in the 1530s. By the early 17th century, it had become the seat of the Casey family; James Casey settled the castle in 1622, though it later passed through marriage to Sir Drury Wray when he wed the eldest daughter of Thomas Casey. The 1654 Civil Survey provides a glimpse of the estate in its heyday, recording not just the castle and bawn but also an orchard, all then owned by Ann Casey, a Protestant landholder during the Commonwealth period.

Archaeological surveys have revealed additional details about the castle’s construction, including evidence of a vaulted third storey in the tower house and the footings of a later residential wing that was added to the east side of the tower, complete with fireplaces on multiple levels. This combination of defensive tower and more comfortable domestic quarters reflects the transition from purely military fortifications to fortified residences that characterised many Irish castles during the late medieval period. The site suffered significant damage during Hurricane Ophelia in October 2017 when portions of the ancient walls finally succumbed to the storm, adding another chapter to the long story of this atmospheric ruin.