On the ground, the enclosure is thoroughly circular, roughly 33 metres across from north to south, and it appears that way on Ordnance Survey maps going back to 1840. The discrepancy is a reminder of how much the eye can be misled by shadows, crop marks, and the angle of a camera, and how differently a landscape reads from the air versus underfoot.

Ringforts, known in Irish as raths, were the standard enclosed farmsteads of early medieval Ireland, typically dating from around the sixth to the twelfth century. They were defined by one or more earthen banks and ditches surrounding a circular interior where a family would have kept livestock and sheltered in timber or wattle buildings. At Knockgraffon, the enclosure follows the classic pattern: an inner bank, now largely worn down to a low scarp, a U-shaped fosse or ditch that was originally considerably deeper than its current 1.66 metres, and an outer bank that survives best in the eastern quadrant. The landowner noted that the fosse had been deliberately built up with earth in the south-east and western sections over the years, obscuring what was once a more pronounced defensive profile. The northern stretch of the outer bank has been partially levelled and is now broad and flat. A causeway crosses the fosse in the north quadrant, likely a later infill rather than an original feature, since there is no corresponding gap in the outer bank. The entrance, just over three metres wide and set into the southern quadrant, is flanked by two limestone boulders with flat faces turned deliberately inward to line the passageway, one on each side of the threshold. These stones, one considerably larger than the other, give the entrance a formality that the surrounding earthworks, worn and partially slighted, no longer quite convey. Silage has been dumped onto part of the outer bank in the south quadrant, a section that had already disappeared from the map by the early twentieth century.