Built by the O’Hallinans on the east bank of the River Deel, this imposing tower house measures roughly 10.65 metres by 5.15 metres, with walls over 2 metres thick that once rose even higher than their current 16.75 metres. The castle’s sophisticated design includes five floors with vaulted ceilings over the second and fourth levels, bartizans containing rooms at the east and west corners of the fifth storey, and a spiral staircase in the north corner that originally connected all levels.

The castle’s tumultuous history reflects the broader conflicts of medieval and early modern Ireland. After being surrendered to the English in 1569, it passed into the hands of the MacSheehy family, who had originally served as mercenaries for the Earls of Desmond. The year 1600 brought particular drama when Dermod O’Connor, having conspired with Sir George Carew to capture James Fitzgerald, the pretending Earl of Desmond, seized the castle from Rory MacSheehy. O’Connor’s victory proved short lived; supporters of the Sugan Earl soon besieged him there and forced his surrender. The castle’s strategic importance is evident from its frequent appearance in historical records, including mentions of Eugene MacSheehy being slain in rebellion in 1580 and his widow Johanna Bourke’s subsequent dealings with the property.

By the mid seventeenth century, ownership had shifted again, with the 1654;56 Civil Survey recording Ellen Butler, an Irish Catholic, as proprietor of Ballyallinan’s lands, which included not just the castle but also an orchard and grist mill. The property was subsequently sold to Lieutenant John Odell for £85 sterling, though various parties contested ownership claims. Classified as a Type 5 Tower House, Ballyallinan represents a unique architectural response within the Irish Gothic tower house tradition, its rectangular floor plan and distinctive features marking it as a significant example of late medieval fortification in County Limerick.