The earliest detailed account comes from 1612, when Robert Dillon of Cannorstown received a substantial grant that included a castle, twenty houses, twelve gardens, a watermill, and a plowland. This grant changed hands several times over the following years; in 1619, Edmond Malone and Teige O’Higgan surrendered the property to King James I, including the stone castle and watermill. That same year, the King confirmed Malone’s grant of Kilgarvan, which encompassed the Kilbillaghan castle along with twelve messuages, a watermill, and various parcels of land measured in cartrons, an old Irish unit of land measurement.

Despite these detailed records, the exact location of Kilbillaghan Castle remains a mystery. By 1837, when the Ordnance Survey teams were documenting Ireland’s landscape, no physical traces of the castle remained visible, though local tradition maintained that it had been a stronghold of the O’Melaghlins, referring to it as Kilbillaghan Castle. The oral history of the area kept the memory alive even as the stones themselves disappeared.

The most intriguing clue to the castle’s possible location emerged in 1981, when investigators noted that the owner of the derelict Newbridge House believed the castle might have stood on that very site. Newbridge House itself, an 18th century two storey structure with four bays and a northern wing, contains an unusual architectural feature: a vaulted ceiling in the lowest floor of the wing, springing from each corner of the room. While this plastered vault dates to the 17th or 18th century rather than medieval times, its presence in such a modest house is peculiar enough to suggest that earlier structures may have influenced the building’s design, or that materials from the lost castle were incorporated into the later dwelling.