Built around 1850, the current house may incorporate stonework from the original castle, though centuries of rebuilding have obscured most traces of the medieval structure. The Down Survey maps from the 1650s show a tower house standing on the western side of the main highway from Athlone to Dublin, on lands belonging to John Dillon of 'Killenenine', with the nearby Walterstown Castle visible to the west along the same road.

By 1837, the Ordnance Survey recorded a T-shaped building here, still bearing the name Killininneen Castle. The surveyors noted the structure measured roughly 20 metres long by 8 metres wide and was already in ruins. When the OS revisited in 1913, they found the castle had been replaced by an irregular-shaped building with a much larger footprint; the new Killininneen House and its associated farm buildings.

Today, no visible remains of the medieval castle survive above ground. Local tradition maintains that the house and outbuildings sit directly atop the castle's foundations, and whilst some farm buildings may have been constructed using stone robbed from the old fortress, no distinctive cut stone from the original structure can be identified. The transformation from defensive stronghold to Georgian farmhouse represents a common pattern across the Irish midlands, where practical Victorian landowners recycled ancient fortifications into more comfortable domestic arrangements.