A ringfort, known in Irish as a rath, is a roughly circular enclosure defined by one or more earthen banks and ditches, used during the early medieval period, broadly the fifth to twelfth centuries, as a farmstead or place of domestic security. The one at Derrishal sits on a gentle north-west-facing slope in pasture, its roughly circular interior measuring about 22 metres east to west. What makes it structurally interesting is its double-bank arrangement: an inner earthen bank, an intervening fosse or ditch, and then a lower outer bank beyond that. Double-ditched ringforts are generally considered to denote higher-status enclosures, and the fosse here survives continuously around the circuit, best preserved where the outer bank also remains intact.

The outer bank, standing only about 0.3 metres above the surrounding ground on its exterior, has been absorbed into the local field boundary system along its north-west to north-east arc, which is a common fate for earthworks that remained visible and useful to later farmers. The inner bank is more substantial, reaching close to a metre in height on its exterior along the eastern to south-south-western stretch, though it drops away to almost nothing on the north-north-eastern side. There are three gaps in the inner bank, the widest at 4 metres on the west-north-west, which may represent original entrances or later breaks. The interior is raised relative to the surrounding ground, and the whole site, banks, fosse, and interior alike, is now overgrown with trees. The detail that anchors the site most firmly to a later chapter of history is a limekiln shown on the western side of the ringfort on the Ordnance Survey six-inch map of 1842. A limekiln was a small stone or brick furnace used to burn limestone and produce quicklime for agricultural use, a common feature of the nineteenth-century Irish landscape. Its positioning here, immediately beside an ancient earthwork, is a reminder of how practical necessity repeatedly overrode any sense of these places as untouchable monuments.