The rectangular four-storey structure, measuring 10.6 metres north to south and 7.5 metres east to west, was once home to Miler McGrath, who served as Archbishop of Cashel from 1570 to 1622. Built from roughly coursed rubble limestone with dressed quoin stones and a defensive base-batter, the tower still bears traces of its original external render and, most impressively, retains its medieval wall-walk and crenellations almost completely intact.

The tower’s defensive features tell a story of medieval Irish architecture at its most practical. The original entrance, now blocked up, sits in the centre of the north wall and once led visitors through a carefully designed security system. Anyone entering would pass through a lobby area overlooked by a murder hole, then into a second lobby before reaching the spiral staircase tucked into the northeast corner. From these stairs, residents could access all the upper chambers and the wall-walk. Whilst the interior has been heavily modified for modern living, intriguing medieval details remain visible from the outside, including an ogee-headed window with decorated spandrels at first-floor level on the south wall, later joined by 18th-century Gothic-style pointed windows.

The castle’s evolution through the centuries is evident in its various additions and modifications. A possible bawn wall, about 0.6 metres thick, extends eastward from the southeast corner of the tower and has been incorporated into a 19th-century castellated farmyard wall; its tall gateway, measuring 2.7 metres wide and 3.65 metres high, may well be the original bawn entrance. An early 19th-century annexe has been added to the west side of the tower, whilst the chimney stack visible at battlement level on the north wall once serviced a medieval fireplace. Despite these changes, Killough Castle remains a striking example of how Ireland’s tower houses have adapted to survive, continuing to serve as a dwelling house whilst preserving their essential medieval character.