Its existence is known almost entirely from a cropmark, the faint differential in vegetation growth that betrays a filled-in ditch below the surface, visible only in aerial imagery captured via Google Earth in July 2018. The enclosure is substantial, measuring roughly 78 metres north to south and 74 metres east to west, dimensions that place it well above the scale of an ordinary ringfort. A single fosse, that is, a ditch that would originally have defined and defended the perimeter, appears to account for the full circuit.

The site was first identified by Simon Dowling, working from satellite imagery rather than ground survey. Two features of the cropmark are worth noting. On the eastern side, the line of the ancient perimeter has been absorbed into a north-south field bank, suggesting that at some point the boundary was reused or respected by later agricultural organisation, even after the original structure had long since silted and grassed over. At the north-east there is a gap of around 20 metres in the visible circuit, which may represent an original entrance. When a water-mains was laid approximately 35 metres to the west, archaeological monitoring carried out by Y. Whitty produced no material related to the enclosure, leaving its date and function unresolved. Large enclosures of this kind are sometimes associated with early medieval activity, occasionally with earlier prehistoric use, but without excavation within the circuit itself, nothing firmer can be said about Kilcannon specifically.