What survives is a roughly 25-metre enclosure, its perimeter marked on the southern, western, and northern sides by an earthen bank topped with hedge, while the eastern edge drops away as a scarp about a metre high. Traces of an outer fosse, the defensive ditch that would once have ringed the whole structure, are still legible on the north-western and north-eastern arcs. A stone field wall, added at some point long after the enclosure's original purpose had been forgotten, cuts across the south-western to north-western stretch of the perimeter.

This kind of earthwork is generally classified as a rath, the Irish term for a ringfort, the most numerous class of monument in the Irish countryside. Ringforts were typically built and occupied during the early medieval period, roughly the fifth to twelfth centuries, and served as enclosed farmsteads for families of middling rank. The Kilnaclay example sits just off the summit of an east-west drumlin ridge, a position that would have given a commanding view down the eastern slope while keeping the enclosure itself from being fully skylined. The most likely entrance, about one and a half metres wide at its base, faces east-south-east, opening toward that slope. What makes the site quietly notable is that it does not stand alone: another rath lies approximately 80 metres to the west-south-west, suggesting that this stretch of drumlin country once carried a small cluster of enclosed settlements, each occupying its own carefully chosen position along the ridge.