This tower house, once part of the lands belonging to James Tobyn of Killahe according to the Ormond Deeds of 1584, now shares its space with a 19th-century farmhouse and serves partly as a storage shed. The Civil Survey of 1654-6 records that the castle was under the proprietorship of ‘James Tobyn of Killaghy Esqr. Irish Papist’ in 1640, marking it as one of the many fortified residences that dotted the Irish landscape during this turbulent period.

Built from roughly coursed sandstone rubble with a distinctive base batter, the tower house measures approximately 5.2 metres north to south and just under 7 metres east to west internally. What remains today includes the modified ground floor, the first floor beneath its original pointed vault, and a fragment of the northwest angle of the second floor. The original entrance, no longer in its original position, appears to have been located at the northern end of the eastern wall; its pointed doorway, complete with a yett-hole at the apex, has been repurposed as an entrance to a farm building about 10 metres to the southwest. The doorway’s construction, largely of limestone with external double chamfer and punch tooling within drafted margins, speaks to the craftsmanship of its medieval builders.

The ground floor, though heavily altered over the centuries, still reveals traces of its original design through blocked window embrasures with crude segmental heads in the southern and northern walls. A mural staircase, now inaccessible but still visible from outside, rises within the eastern wall from its northern end. Evidence suggests there was once a second floor beneath the vault, indicated by a blocked window within a large splayed embrasure in the western wall. While time and agricultural repurposing have taken their toll on this once-formidable structure, Castle John remains a tangible link to the complex history of land ownership and religious identity in 17th-century Ireland.