It bears the inscription "Anno Dom 1627 N H", and it once formed part of Killyon Manor, a fortified house and bawn that has since been levelled entirely. A bawn was the walled enclosure that typically surrounded an Irish tower house or plantation-era dwelling, serving both as a defensive perimeter and a yard for livestock. That the datestone survived at all, salvaged and reset into an otherwise unremarkable building, makes it one of the few physical traces of a structure that, by mid-seventeenth-century accounts, was substantial enough to warrant detailed description.

When the antiquarian Cooke wrote about Killyon Castle in 1875, drawing on earlier records, he described a large square gatehouse opening onto a courtyard, with small round flanking towers still showing gun loops, the narrow angled slits designed to allow firearms to be aimed outward while protecting the shooter. By 1634, according to Cooke, the site was occupied by a person named Herbert, or Harbart as the name was also rendered, and the initials N H on the datestone may plausibly connect to that same family, though the notes do not confirm this directly. The manor itself was believed locally to have been constructed on the site of something far older: a nunnery said to have been founded at Killiadhuin, the earlier name for Killyon, by St Ciaran of Saiger in the fifth century. O'Flanagan, writing in 1933, recorded this tradition, and while the continuity between a fifth-century ecclesiastical foundation and a seventeenth-century plantation house cannot be verified archaeologically from what survives, the layering of the claim is characteristic of how Irish sites accumulated histories across centuries.

The datestone itself can now be examined in three dimensions via a photogrammetric model available online at the link associated with this record, which allows close inspection of the carved lettering without requiring a visit to the parish hall corner where it sits, quietly embedded in the masonry.