Once an important stronghold of the O’Connors of Corcomroe, the castle had passed to Sir Donal O’Brien by 1572. The fortification changed hands multiple times during the turbulent first half of the 17th century before meeting its ultimate fate around 1655, when Cromwellian commissioners ordered its dismantling as part of their systematic destruction of Irish castles.

Today, only fragments of this small rectangular tower house remain standing. The northeast corner survives best, with portions of the north and east walls still reaching approximately 6.5 metres in height. Built from uneven limestone masonry courses bound with hard white mortar, the structure originally measured about 3 metres east to west internally, with walls nearly 2 metres thick at the base. Architectural details like the rebate for a loft and the springing point of a vault, visible at 2.3 metres height on the inner east wall face, hint at the building’s former internal arrangements. The castle appears to have been constructed directly on the line of the cashel’s southern wall, integrating the ancient defensive earthwork into its own fortifications.

Archaeological surveys have identified several associated structures nearby, including a possible 16th or 17th century house about 18 metres to the north that may have served as the tighe móir, or main residence, of the cashel complex. Three additional houses lie approximately 23 metres northeast of the tower house ruins. While the exact relationship between these buildings and the castle remains unclear, together they paint a picture of what was once a significant settlement. The site appears on the 1842 Ordnance Survey map as “Ballyganner Castle (in ruins)”, and by the 1897 survey, only the eastern and southern walls were still depicted, surrounded by the substantial rubble mound that visitors see today.