The three-storey structure measures 8.8 metres north to south and 7.8 metres east to west, with distinctive projecting towers at its northwest and southwest corners; one containing a spiral staircase, the other housing a garderobe. The ground floor features a vaulted ceiling accessed through a doorway in the south wall, whilst narrow windows and slits provide minimal lighting throughout. Though time has taken its toll, particularly on the upper staircase which once led to a now-inaccessible second floor, the castle remains a substantial presence in the landscape.

The tower house sits within a remarkable cluster of historical structures that tell the story of Killagh’s past. Just 70 metres to the north stand Killagh Corn Mill and Tuck Mill, whilst 130 metres southeast you’ll find the earthworks of a motte and bailey castle. The medieval church and graveyard lie 150 metres to the east-southeast, creating an unusually complete picture of a medieval Irish settlement. Later additions include an 18th-century house built directly against the castle’s east wall and a pigeon loft incorporated into the south wall’s outer face, showing how the structure continued to serve practical purposes long after its defensive role had ended.

Historical records provide fascinating details about the castle’s survival through turbulent times. The Down Survey map of Killagh parish, drawn in the 1650s, shows the castle annotated as ‘in repaire’ and standing on lands belonging to George Nugent, described as an ‘Irish papist’ in 1641. The accompanying terrier confirms the castle’s relatively good condition at that time, noting it alongside the mills and ruined church as key features of the settlement. This documentation suggests the castle weathered the upheavals of the 17th century better than many of its contemporaries, though derelict 18th-century buildings now abutting its southeast corner hint at later periods of decline and adaptation.