The name is a small puzzle in itself: demesne is a term associated with the managed lands of a landed estate, and attaching it to a prehistoric earthwork suggests the enclosure had become so fixed a feature of the local landscape that later inhabitants simply folded it into their own vocabulary for the land around them.

The fort is a rath, the most common type of enclosed settlement in early medieval Ireland, typically consisting of a circular or near-circular bank and ditch surrounding a domestic space where a farming household would have lived. This particular example is subcircular in plan, measuring roughly 56 metres east to west and 50.5 metres north to south. It is defined by two banks with an intervening fosse, meaning a broad ditched depression between them, which would have made the enclosure considerably more imposing when the earthworks were at their full height. The inner bank survives along the southern and western arcs, while elsewhere the boundary reduces to a scarp, a natural or cut slope in the ground, with a later field wall laid across the northern side. Three causeways cross the fosse at different points, and the southernmost of these is considered a possible original entrance. Also associated with the site is a feature recorded as a possible cashel, a type of stone-walled enclosure that sometimes occurs alongside or overlapping with earthwork raths, though this element remains tentative.