A rath is an early medieval enclosed farmstead, typically defended by one or more earthen banks and ditches, and this one at Drumagelvin preserves its essential form despite centuries of erosion and encroaching vegetation. What remains is a subcircular enclosure measuring approximately 33 metres northeast to southwest and 29 metres northwest to southeast, with an earthen bank that survives most clearly on the southern side, where its base is still around 4.6 metres wide and stands nearly 2.75 metres in external height. Elsewhere the bank has been reduced to a low, overgrown scarp, but the outer fosse, a defensive ditch running around the perimeter, can still be traced. A ramp entrance, roughly 3.9 metres wide at its base, opens to the east.

The site has a cartographic history stretching back over two centuries. It appears on McCrea's Map of County Monaghan, dated 1793, and again on the Ordnance Survey six-inch maps of 1834 and 1907, meaning that each generation of surveyors found it significant enough to mark. Its position on the southern end of a drumlin ridge, those elongated hills of glacially deposited material that ripple across this part of Ulster, would have made it a logical choice for a defended enclosure: slightly elevated, with natural slopes providing additional protection on several sides. The planted trees around the perimeter are a later addition, common on Irish farmland where raths have long been absorbed into field boundaries or treated as awkward but vaguely respected features of the landscape.