Sitting atop a low, oval-shaped drumlin, one of those smooth glacially deposited hills that ripple across the Irish midlands, the ringfort has been so thoroughly levelled that a visitor standing on the ground in 1998 would have found no surface remains whatsoever. The scarp, the sloping earthen edge that once delimited the enclosure, had been worked away until it merged imperceptibly with the natural slope of the ridge itself. Only a band of unusually dark green grass near the base of the ridge on the eastern side hints at what lies beneath, the kind of colour shift that often indicates a backfilled fosse, a defensive ditch that has been filled in but whose disturbed, moisture-retaining soil quietly feeds the grass above it for centuries.

The site was recorded as a fort on the 1837 Ordnance Survey Fair Plan, and appears again on the 1913 twenty-five-inch Ordnance Survey map as a sub-oval earthwork, measuring roughly 40 metres east to west and 65 metres north to south, rising about 2.5 metres above the surrounding pasture. A ringfort or rath, to give it its Irish term, was typically a circular or oval enclosure defined by one or more earthen banks and ditches, used during the early medieval period as a farmstead and the focus of a family's agricultural and domestic life. There are tens of thousands of them recorded across Ireland, but their survival is uneven, and Clonlost represents a case where agricultural pressure has done what centuries of simple neglect did not. A related enclosure lies roughly 95 metres to the north, suggesting this was once part of a broader landscape of early settlement. Aerial photography has since recovered the sub-oval outline of the monument from above, the ground giving up to the camera what it conceals from anyone walking across it.