It is a cashel, the Irish term for a ringfort built from stone rather than earthen banks, and this one measures roughly twenty metres north to south and just over twenty-two metres east to west. At its highest, the enclosing wall now stands only about a metre tall, much of it fallen in on itself over centuries of slow disintegration.

Ringforts of this type were the dominant settlement form in early medieval Ireland, typically serving as enclosed farmsteads for a single family and their livestock. The cashel at Derrynacaheragh follows the broadly circular plan common to the type, though its boundary has not survived intact. To the north-west, the original stone wall has been replaced entirely by a stone-faced field fence, the kind of pragmatic reuse that has altered countless ancient enclosures across the Irish countryside. A later stone wall was added along the north-east section at some point, layering one era of activity on top of another. Two gaps survive in the perimeter, one to the north-north-east, about three metres wide and blocked with loose stones, and a narrower one to the west, measuring roughly one and a half metres across. Whether either represents an original entrance is not certain, but the blocked north-north-north-east gap is the more substantial of the two and a likely candidate.