This limestone tower, which forces modern traffic to divert around it, was originally known as ‘The Queen’s Castle’ on a map dating from around 1600, though it has since undergone several name changes. The structure spans St John’s Street with a pointed arch, creating a gateway that may have served as the town’s original north gate or as a ‘main guard’ during the Elizabethan period.

The three-storey tower is a study in defensive architecture, built from coursed limestone with distinctive long and short quoins at its corners. A protruding rectangular stair turret juts from the north-east side, lit only by narrow defensive slits. The tower’s various floors show different lighting arrangements; the ground floor chamber features rectangular windows with hoodmoulds, possibly later insertions, whilst the upper floors display a mix of pointed and rectangular openings. The structure once topped off with stepped merlons, those tooth-like battlements so characteristic of medieval fortifications, and a drainage course above the third floor helped protect the masonry from Irish weather.

Archaeological excavations in 1999 revealed fascinating details about the castle’s surroundings and the town’s development. Beneath the archway, archaeologists discovered a well-preserved cobbled surface extending southeast, its stones measuring roughly 30cm long by 10cm wide, consistent with road surfaces found elsewhere in medieval Kilmallock. Perhaps most intriguingly, the discovery of what appears to be a defensive ditch suggests that King’s Castle sits on the original northern boundary of the town, predating the later stone walls that enclosed an expanded settlement. The castle’s first historical mention comes from documents dated 1204 to 1206, placing it firmly within the Anglo-Norman period of Irish history, though the current structure likely dates from the 15th or 16th century.