It measures approximately 30 metres north to south and 26 metres east to west, defined by a low bank of stone and earth that, by the time anyone looked closely at it in 1998, had already been reduced to near-invisibility along its north-eastern arc and levelled almost entirely from the east around to the south-east. Later field walls, now themselves removed, had further confused the picture. What survives is partial, eroded, and hemmed in by scrub, with an elongated ridge to the south and higher rocky ground closing off the view to the east.

Enclosures of this general type, circular or near-circular banks that once defined a bounded space, are among the most common archaeological features in the Irish landscape, though their purposes varied considerably. Some were ringforts, the enclosed farmsteads of early medieval Ireland; others served as cattle pounds, burial grounds, or ceremonial spaces. The Ballynalackan example does not, on present evidence, resolve neatly into any one category. What can be said is that it was already recognised as a feature worth mapping by the time the Ordnance Survey produced its six-inch sheets in 1842, where it appears with hachuring, the fine radiating lines surveyors used to indicate a raised or banked earthwork. It was still considered notable enough to appear, at least partially, on the revised edition of 1915, though even then it was only partially indicated, suggesting the erosion now so visible had already been underway for some time.