The rectangular structure, measuring approximately 33 metres north to south and 19 metres east to west, dates from the late medieval period and was already falling into disrepair by the mid-17th century. When Commonwealth surveyors documented the site between 1654 and 1656, they simply noted it as ‘a castle out of repaire’, though records show James Butler held the property in 1640.

Today, visitors can still trace the castle’s substantial limestone walls, built from coursed rubble with walls nearly one and a half metres thick. The eastern wall remains the best preserved, standing to first-floor height alongside the southern wall and portions of the western wall. At the northeast corner, the remnants of what appears to have been a tower show distinctive base-batter construction, a defensive feature common in Irish tower houses. A peculiar architectural detail catches the eye here: a stone projection extending eastward from the external face contains a segmental-arched embrasure, likely part of the original tower’s defensive architecture.

The castle’s interior features have largely vanished with time, though evidence of a destroyed doorway remains visible at first-floor level in the centre of the eastern wall, which would have provided access to the northeastern tower. Unlike many Irish castles of this period, Castletown shows no archaeological evidence of an attached bawn, the defensive courtyard wall that typically enclosed castle grounds. Set against the undulating Tipperary countryside, these lonely ruins offer a glimpse into the region’s turbulent past, when such fortified residences dotted the landscape of Gaelic and Anglo-Norman Ireland.