The enclosure at Johnstown, in the old barony of Balrothery East, came to light not through any targeted archaeological investigation but as a routine precaution ahead of a proposed landfill development, the kind of discovery that happens quietly, in the margins of paperwork, and might easily have gone unrecorded.

In 2005, a geophysical survey was carried out under licence (05R062) across the proposed development area. Geophysical survey works by detecting anomalies in the soil's magnetic or electrical properties without breaking the ground, essentially reading the archaeology from the surface. What the survey revealed was a sub-circular enclosure roughly 40 metres in diameter, along with what appeared to be possible internal features. The findings were documented by Lohan in 2006. Enclosures of this broad type are among the most common monuments in the Irish landscape, ranging from early medieval ringforts, which were enclosed farmsteads, to prehistoric ritual sites, and without excavation it is not possible to say which category this one belongs to or what period it dates from. The internal features, equally uncharacterised, add a further layer of ambiguity.

Because the site was identified through geophysical survey rather than excavation, there is nothing visible at ground level. The enclosure lies beneath the surface, its outline legible only as a pattern of soil differences recorded on a specialist's report. The area is in the Johnstown townland, within the Balrothery East barony, north County Dublin, though the precise field location is not publicly mapped in a way that makes casual visiting straightforward. For anyone with a particular interest in the archaeology of the Dublin hinterland, the record sits in the published survey literature and serves as a reminder of how many features of this kind remain unexamined, their function and date still open questions waiting on some future intervention.