Historical records show the Butlers held the castle and estate from at least 1560 until 1698, when they granted it to a Scottish gentleman named Mr. Hely, whose descendants became the subsequent proprietors. The tower house, measuring approximately 13.5 by 10.8 metres, was constructed from roughly coursed limestone rubble with carefully dressed corner stones and features a distinctive sloping base, known as a base-batter, that rises nearly three metres high.

The castle’s defensive architecture reveals the turbulent times in which it was built. Entry was through a pointed doorway on the eastern wall, now blocked with masonry, which led to an entrance lobby protected by a murder hole above and a cross-loop opposite; classic defensive features that allowed defenders to attack intruders from relative safety. A guard room sat immediately to the north, whilst a spiral staircase in the southeast corner provided access to all floors. The tower’s walls contain numerous mural chambers and passages, including one on the first floor that gave access to the murder hole. Each floor was lit by an assortment of windows; some single, others with two lights, featuring flat, round, and ogee-headed designs with external chamfers. The more elaborate windows, such as the two-light ogee-headed window on the fourth floor’s south wall with its hollow spandrels, demonstrate the castle’s dual purpose as both fortress and residence.

Today, much of the parapet has collapsed, though sections survive on the south face and southeast angle where evidence suggests a possible cap house once stood. A high chimney stack still rises from the western end of the south wall, and traces of external harling, a type of rough-cast rendering, can be seen on the walls. The north wall bears the ghostly outline of a steep-pitched roofline from an external building that once stood against the tower, accessed through two doorways that were later broken through the wall. Whilst time has taken its toll on this riverside stronghold, with a collapsed vault over the third floor and a visible crack running up the north face, Foulkscourt Castle remains an impressive testament to medieval Irish castle building and the complex history of land ownership in Kilkenny.