Located just 25 metres from Rathcool motte and within sight of the local church and graveyard, this site was once home to a substantial fortification. The Civil Survey of 1654-56 paints a vivid picture of the estate in its heyday, describing not only a castle but also a thatched house, an old orchard, gardens, and several small cottages, all bisected by the Glassalin rivulet. The property belonged to James, Lord Baron of Dunboyne, recorded as an ‘Irish Papist’ proprietor in 1640.

Today, visitors to Rathcoole House will find that the modern buildings incorporate what little remains of the medieval castle, likely a tower house. One wall of the original structure survives, standing two storeys high and measuring 1.7 metres thick, with its distinctive external base batter still visible on the north-facing side. This wall now stands 2.2 metres from the southern end of a two-storey house, where it connects to a later three-storey addition. The rest of the castle appears to have been completely levelled, though the surviving wall may have been preserved because the 17th-century thatched house mentioned in historical records was built directly against it.

Recent renovations have yielded an unexpected treasure; workers discovered the central portion of an ogee two-light cut limestone window head, probably dating from the 16th century, built into the chimney stonework of the two-storey house. This architectural fragment offers a tantalising glimpse of the castle’s former elegance. The current two-storey house, running roughly north to south, may well be the same thatched dwelling documented in the Civil Survey, representing an unusual example of architectural continuity spanning nearly four centuries.