The earthwork at Ballynacourty is a rath, the Irish term for a ringfort, which was the standard form of rural enclosure used across early medieval Ireland, broadly from around the fifth to the twelfth centuries. Thousands of them survive in various states of decay across the country; this one is notable for how much of its structure can still be read on the ground.

The ringfort forms an almost exactly circular enclosure, measuring 40.7 metres north to south and 41 metres east to west. It is defined by an earthen bank that, on its exterior face, still stands to a height of just over two metres along its best-preserved arc, running from the south-west around to the north-north-west. That outer height is significant; it suggests the bank was once a meaningful barrier rather than a purely symbolic boundary. Beyond the bank lies a fosse, the external ditch that was dug to provide the material for the bank itself, and beyond that again a low counterscarp bank of earth and stone. The fosse survives most clearly along the western arc but has largely silted up elsewhere over the centuries. A causeway entrance, 3.75 metres wide, breaks the circuit at the south-south-west, which was likely the original approach point into the enclosure. At some later date, a dry-stone field wall was built directly across the fosse and along the top of the bank between the north-north-west and north-east, an intrusion that speaks to the site's long afterlife as working farmland rather than monument. Inside, the ground slopes gently downward to the east, and faint cultivation ridges are still visible running on a rough north to south axis, suggesting the interior was worked at some point after the original occupation. The site was recorded by Denis Power and uploaded to the national monuments record in August 2011.

The ringfort sits in open pasture, so the earthworks are most legible in low winter light or on a clear morning when shadows fall across the banks and bring the topography into relief. The causeway entrance at the south-south-west is the clearest point of orientation once you are on site. The section of bank running from the south-west to the north-north-west gives the best sense of the original scale, while the field wall cutting through the fosse is a useful reminder of how thoroughly later agricultural life has rearranged even the most substantial early medieval remains.