The squat tower house was likely built by the O’Connors in the 14th or 15th century, originally standing as a defensive structure with its own bawn wall. Today, the castle rises approximately 9.3 metres high and sits atop elevated ground with commanding views across the Offaly countryside; on clear days you can spot Croghan Hill to the west and the boglands of Coole stretching to the south.

The castle underwent dramatic transformations when the Nesbitt family built Toberdaly House in the mid-18th century, incorporating the medieval tower into their grand design. They raised the ground around the north and east sides to create formal gardens measuring roughly 46 by 35 metres, transforming the old fortress into a decorative corner feature. In a particularly creative adaptation, they relocated the original ground floor doorway to the second floor to provide access to an octagonal gazebo built atop the tower, whilst converting the interior into a dovecote complete with stone nesting boxes. The original entrance, protected by an iron yett (a type of defensive grating), can still be traced in the blocked doorway of the east wall, complete with its yett hole and pintle holes that once held the heavy iron hinges.

The tower’s complex internal layout reveals its layered history. The ground floor chamber, measuring 5.45 by 5.2 metres, was accessed through a lobby area protected by a small guard room in the northeast angle. An unusual L-shaped floor plan on the upper levels suggests the spiral staircase in the southeast corner was added to an earlier structure, whilst evidence of altered floor levels and a 16th century barrel vault insertion point to significant rebuilding phases. Following the burning of Toberdaly House during the Irish Civil War in April 1923, only the south wall of the grand house remains standing, leaving the medieval tower as the primary survivor of this once-impressive estate.