The castle’s name likely derives from Cluain siar, meaning “western meadow”, though early records from 1201 spell it as Cluonsiebra, suggesting alternative origins. Throughout the Middle Ages, these lands belonged to the church, with the Bishops of Limerick developing both the castle and a nearby settlement that included at least five burgages by 1252. The 1658 Down Survey map shows the castle alongside a watermill on the east bank of the river, with the opposing townland marked as “Graig bishop town”, further evidence of the church’s enduring influence over this area.

The castle itself is a fascinating example of multi-period construction, with three distinct building phases spanning from the 13th or 14th century through to the post-1700 period. At its core stands a four-storey rectangular keep measuring approximately 9.2 by 6.5 metres externally, with walls 1.3 metres thick. The original structure comprised just the lower two floors of this keep, which was later heightened when a five-floor stair turret was added to the west side in the late 15th or 16th century. This turret, built from dressed limestone masonry, contains a finely carved spiral staircase lit by flat-arched, chamfered windows. A three-floor eastern addition completed the complex, whilst a now-ruined three-storey structure once stood in the south-west angle between the turret and keep.

The interior reveals sophisticated medieval craftsmanship and domestic arrangements. The ground floor features a pointed barrel vault, whilst upper floors once held fireplaces, wall cupboards, and elegant ogee-headed windows with hollow spandrels and window seats. Particularly intriguing is a stone basin set into a double-splayed recess near what may have been a chapel, supporting local tradition about religious use within the castle. The property changed hands several times during the turbulent 17th century; James Crowe held it in 1641, followed by Captain William Piggott in 1655 through his wife’s claim, and Captain Thomas Walcott controlled it along with a mill by 1659. Though time has taken its toll, with collapsed walls and missing floors, Clonshire Castle remains an impressive testament to medieval Irish architecture and the enduring power of the church in shaping the landscape of County Limerick.