The ground at Corrageen gives nothing away; the pasture is smooth, unbroken, and entirely unremarkable to the eye. Yet the Ordnance Survey's six-inch map of 1839 recorded something here, marking a faint rectangular outline and labelling it plainly as a 'Site of fort', roughly 45 metres from north-west to south-east and about 35 metres across. That modest annotation is, at this point, the entirety of the physical evidence.

The Ordnance Survey's first Irish mapping project, carried out in the 1830s, was unusually diligent about recording antiquities alongside topographical features, which is why so many sites known only through that source still carry their ghostly designations into the present. What the surveyors observed at Corrageen, whether earthworks, banks, or some trace of a ditch, has since been lost entirely to agriculture or natural erosion. An enclosure of these proportions would typically be interpreted as a ringfort or enclosed settlement of early medieval date, the kind of site that once dotted the Irish countryside in enormous numbers and that continued to be levelled well into the twentieth century. The rectangular form here is somewhat less common than the circular ringfort, though rectangular enclosures are not unknown and may reflect a different period or function.