The Down Survey barony map of Fore, drawn between 1656 and 1658, shows the castle as a tower perched on a hill, marking its importance in the local landscape. By the time of the Civil Survey just a few years earlier, the property belonged to Christopher Earle of Fingal, who held 550 acres here. His holdings included not just the castle with its protective bawn wall, but also a ruined church, six small dwellings, a corn mill and a tucking mill for processing cloth; quite the rural enterprise for its day.

Today, visitors won't find the castle marked on modern Ordnance Survey maps, but archaeological investigation has revealed tantalising traces of the past. A section of masonry wall, exposed through excavation on a slight rise in the terrain, is believed to be all that remains of the castle structure itself. The site forms part of a medieval complex that includes a motte approximately 75 metres to the south and the church ruins about 100 metres to the east-southeast, suggesting this was once a thriving medieval settlement.

The castle's disappearance from the physical landscape whilst remaining documented in historical records offers a glimpse into how dramatically Ireland's built heritage has changed over the centuries. From Christopher Earle's substantial estate with its working mills and defensive structures to barely visible wall foundations, the site at Killallon demonstrates how even substantial stone buildings can vanish almost completely, leaving only historical documents and careful archaeological work to piece together their stories.