This intriguing structure first appears on the Down Survey barony map of Deece from 1656-8, depicted as a roofed, gabled building. The Civil Survey records from 1654-6 reveal that in 1640, the property belonged to Josaline Usher, who owned 169 acres that included both a stone house and a church. Today, what remains is an oblong structure measuring 18.5 metres north to south and just over 3 metres east to west, its original entrance still visible as a lintelled doorway near the northern end of the eastern wall.

The castle’s most remarkable feature is its barrel-vaulted ceiling, which still shows traces of the wicker-centring used in its construction; a fascinating glimpse into medieval building techniques. Over the centuries, the vault has been covered by an earthen mound now thick with vegetation, giving the structure an almost hidden quality in the landscape. The interior space has been subdivided into five separate chambers by walls added after the original construction, suggesting the building’s use evolved over time to meet changing needs.

Positioned on level ground about 80 metres east of a south-southeast to north-northwest section of the River Boyne, Balsoon Castle sits in close proximity to the parish church of Balsoon, located roughly 60 metres to the north. By 1908, when it appeared on the Ordnance Survey 6-inch map, it was still recorded as an oblong structure, maintaining its distinctive footprint despite the passage of more than 250 years since its first cartographic appearance.