Its most telling detail is the way its boundary wall has been cannibalised by later farmers: the drystone-faced earth and stone bank that defines the eastern, southern, and western arcs of the site has been folded into the adjoining field boundaries, so that what was once a self-contained enclosure now does double duty as ordinary agricultural walling. The northern side is a simpler, lower earthen bank, and there is no fosse, the term for the external ditch that commonly accompanies this type of monument. That absence gives the site an unusually clean, unfurrowed profile.

The enclosure is a rath, the Irish term for a ringfort, a class of monument built across Ireland roughly between the early medieval period and the Viking Age, from around the fifth to the twelfth century. They functioned primarily as enclosed farmsteads, the bank and any associated fence or hedge marking the boundary of a household's living and working space rather than a military fortification in any serious sense. This one at Knockatomcoyle measures thirty-three metres in diameter, placing it within the typical range for single-banked examples. The entrance, two metres wide, faces north-east. Inside, the north-east quadrant preserves traces of a circular hut or house foundation about four and a half metres across, the kind of structure that would once have sheltered a family or their livestock. A low mound, approximately six metres by three and a half metres, sits against the inner face of the bank on the north-west side; its purpose is unrecorded, though such features within ringforts have in other cases represented storage areas, collapsed structures, or accumulated domestic debris.

Because the banks have been integrated into working field boundaries, the enclosure is most legible from ground level when vegetation is low and the subtle changes in earthwork height can be read against the slope. The drystone facing on the main bank is the sharpest indicator that this is something older than the fields it now appears to belong to.