That this earthwork survives at all, legible from aerial imagery as recently as 2013, owes something to accident and something to the particular stubbornness of early Irish enclosures in the landscape.

The fort at Tullycarragh occupies the crest of a drumlin ridge, that characteristic hummock of glacially deposited material that gives Monaghan and its neighbouring counties their rolling, lumpy terrain. The enclosure is roughly circular, perhaps tending toward a D-shape, and measures approximately 30 metres along its north-west to south-east axis and around 25 metres across. It is defined by an earthen bank faced with stone on the outer side, with traces of an inner stone facing as well. The bank itself is modest, standing just over a metre high on the exterior at the northern arc, and around 0.6 metres on the interior. There is no visible fosse, which is the term for the external ditch that commonly accompanies such earthworks, though its absence does not necessarily indicate that one never existed. The entrance, roughly 2 metres wide at the base, opens to the south-east, a common enough orientation for enclosures of this type, possibly related to morning light or to the practical logic of the surrounding terrain.