A ringfort, or rath, was a roughly circular enclosure of earthen banks, typically built during the first millennium AD as a defended farmstead, and the one at Knockdrislagh has been reduced to almost nothing. What remains is an oval depression to the east, the ghost of the original fosse or ditch, and a low rise along the northern and western arc of the enclosure, partly absorbed into the surrounding field boundaries. The site measures approximately 27 metres north to south and nearly 23 metres east to west.

The history of its disappearance is documented in stages. On the Ordnance Survey six-inch map of 1842, the fort appears as a clear hachured circle, the conventional cartographic mark for an earthwork. By the 1904 and 1938 editions it had already been drawn into the field system along its northern edge and showed a gap to the south-south-east, suggesting gradual incorporation into agricultural land. Bowman recorded it in 1934 as standing on land belonging to an Elizabeth MacSweeney, noting it was by then practically levelled, with a diameter of roughly twenty-five yards. Local accounts hold that whatever remained was finally cleared around 1962. The sequence maps a process that played out across rural Ireland throughout the twentieth century, as earthworks that had endured for over a thousand years were removed to consolidate farmland.

The site sits in pasture and there is little to see without knowing what to look for. The slight eastern depression is the most legible surviving feature, and the low ground-level rise along the north-western arc becomes more readable in low, raking light, particularly in winter or early morning when shadows fall across the grass at an angle.