The Ordnance Survey mapped it twice, in 1836 and again in 1908, each time marking it not as a fort but as the site of one, that careful cartographic hedge indicating something already lost or at least very nearly so. What the mapmakers recorded was a circular embanked feature roughly 38 metres in external diameter, the kind of earthwork that in Ireland typically signals a ringfort, a type of enclosed farmstead used from the early medieval period onward, defined by a bank and ditch encircling a domestic or agricultural space.

By the time a field inspection was carried out in 1968, the feature had contracted or degraded considerably. What remained was a subcircular, grass-covered area measuring approximately 22.7 metres north to south and 19 metres east to west, defined not by a clear bank but by a scarp, essentially a slope or step in the ground surface, ranging from about half a metre high on the southern side to just over a metre on the western. A fosse, the ditch that would once have run around the outside of the enclosure, was still faintly traceable on the southern side, though it had effectively disappeared on the west. No entrance could be identified. The discrepancy between the 38-metre diameter shown on the nineteenth-century maps and the much smaller dimensions recorded a century later suggests either significant erosion over that period or that the earlier cartography was capturing a wider earthwork complex that fieldwork could no longer confirm on the ground.

What makes Rathkenny quietly interesting is precisely this layered uncertainty. The site sits at the bottom of a slope rather than on a commanding height, which is itself a little unusual for a monument of this type, and successive attempts to pin it down have produced measurements that do not quite agree. It persists in the record as a parenthetical, always a site of something rather than the thing itself.