This is a rath, a type of enclosed settlement once common across early medieval Ireland, typically defined by one or more earthen banks and used as a farmstead by a family of some local standing. At Kilnagreban, the enclosing element survives only partially as a built bank; elsewhere it has flattened into a scarp, a slope in the ground rather than a distinct raised feature.

The monument is oval in plan, measuring roughly 25 metres north to south and 14 metres east to west. Where the bank survives, between the east-south-east and south-west arcs, it reaches just under a metre in internal height and is less than that on the outer face, with a width of around 1.9 metres. These are modest dimensions, and the structure is described as very poorly preserved. Vegetation has accumulated heavily along the south-eastern to north-western stretch, further obscuring whatever remains of the original earthwork beneath. The combination of partial collapse, scrub encroachment, and the general softening of the landform over centuries has left Kilnagreban in the condition common to many raths that never attracted later reuse or attention.