Built by the O’Duigin family in 1636, this four-storey rubble-built tower house features a distinctive projecting tower at the centre of its south wall. Though time has taken its toll, with the north wall now destroyed, the castle still displays many of its original defensive features, including a machicolation positioned above the doorway and three water spouts extending from the top of the south wall. The surviving east and west gables retain their chimney stacks, whilst the east gable preserves fireplaces on the first, second and third floors, along with rectangular limestone windows adorned with chamfered edges.

The castle wasn’t built in isolation; it formed part of a larger defensive complex. Remnants of a rectangular bawn wall, complete with splayed gun loops for musket defence, can still be traced around the site, with outbuildings visible in the northeast corner. A gatehouse once stood at the centre of the south bawn wall, providing controlled access to the fortified enclosure. These features were typical of plantation-era castles, designed to protect landowners during a turbulent period in Irish history.

The castle’s datestone, which bears the inscription ‘I.H.S. 1636 I.N.R.I. JOHN’, no longer resides at Cloncourse. It was relocated to nearby Mondrehid House, which was constructed close to the site of another castle, Mondrehid Castle. This carved stone serves as a tangible link to the O’Duigin family and their role in the complex tapestry of 17th-century Laois, when fortified houses like Cloncourse represented both homes and strongholds in an uncertain landscape.