When the Ordnance Survey mapped the area in 1842, the site appeared as a complete hachured circle, roughly 35 metres across, the standard notation for a raised circular enclosure. By 1904 and again by 1938, successive editions of the same maps recorded that the bank along the north-eastern to southern arc had been levelled, absorbed into the working landscape of a farm.

Ringforts, known in Irish as raths when defined primarily by earthen banks and ditches, were the typical enclosed farmsteads of early medieval Ireland, built and occupied roughly between the fifth and twelfth centuries. Thousands survive across the country in varying states. What makes the Grenagh example useful as a case study is how legibly the OS mapping sequence traces its partial removal. What had been a coherent circuit became, over the course of a century, a fragment. Today, an arc of earthen bank running from the north-west to the north-east still stands to an internal height of about 1.6 metres, with an external fosse, a shallow defensive or drainage ditch, surviving to a depth of 0.55 metres. On the south-western to north-western side, an outer bank reaching 1.7 metres in height remains, though it has been folded into the modern field fence system rather than preserved in isolation. That incorporation is itself a reminder of how often the boundaries of ancient enclosures ended up doubling as convenient field divisions long after their original purpose was forgotten.