When archaeologists inspected it in 1989, the interior, roughly 24 metres across, was already heavily overgrown with scrub and trees, and no way in could be identified. The bank itself, a low ring of earth and stone running about three metres wide and standing just over a metre high, is the kind of feature that a passing driver would register only as a slightly thickened hedgerow.

Enclosures of this type are generally understood to be ringforts, the most common field monument in Ireland, built primarily during the early medieval period, roughly the fifth to twelfth centuries, as enclosed farmsteads for single family units. The earthen bank, known in Irish archaeology as a rath, would originally have been topped with a timber palisade or thorn hedge to keep livestock in and wolves out, with a single formal entrance facing, in most cases, to the east or south. The Coolroe example appeared on the first edition Ordnance Survey six-inch map of 1839 as a clean circle of around 30 metres in diameter, suggesting it was still a recognisable feature in the landscape at that point. By the time of the 1900 to 1901 revision, the cartographers were rendering it differently, as a subcircular outline defined by short straight lengths, possibly reflecting how the overgrowth and encroaching vegetation were already beginning to blur its edges. A public road running northwest to southeast clips the outer edge of the north-northeast sector, which may account for some loss of the bank on that side and complicates any straightforward reading of its original form.