The castle’s strategic position places it 60 metres northeast of Knocklong church and graveyard, which occupy higher ground to the southwest. Built in at least two distinct phases, this multi-period structure reveals its complex history through its varied masonry and architectural features.

The earlier northern section of the castle displays notably different construction from its southern half, with walls reaching 2.5 metres thick compared to 1.5 to 1.9 metres elsewhere. The original medieval structure, measuring approximately 11.1 metres north to south by 9.1 metres east to west externally, featured a stone vaulted ground floor entered through an off-centre doorway in the east wall, complete with a drawbar slot for security. A particularly fine late medieval twin-light ogee-headed window with decorated spandrels survives high in the west wall at second floor level, whilst a garderobe chute in the northwest angle served the first floor. Evidence suggests the castle underwent significant modifications during the 17th century, when the stone vault was replaced with wooden floors, the south wall was heightened with a chimney stack, and a two-storey house was added to the eastern side.

Historical records trace the castle’s ownership through several centuries of Irish history. The Desmond Survey of 1584 noted Garrett mcThomas as the free tenant of the castle and village of Knocklong, whilst Thomas O’Hurley owed various dues to the Earl of Desmond from the surrounding lands. By the time of the Civil Survey in 1654-56, Sir Maurice Hurley, described as an Irish Papist, possessed the then-ruined castle along with a mill, two fairs, and court rights. The castle’s strategic and economic importance to the local area is evident from these documents, which show it served not just as a defensive structure but as the administrative centre for the surrounding territory. Today, though partially robbed of its quoins and lower courses on the western side, the castle remains an impressive reminder of the complex layers of Irish medieval and early modern history.