Drumlins are the smooth, elongated hills left behind by retreating glaciers, and across the Irish midlands they were frequently chosen as the sites of ringforts, the enclosed farmsteads and defended enclosures of early medieval Ireland. This one at Corrinagh makes use of the natural elevation with some deliberateness.

The fort measures 42 metres in diameter across its raised interior platform, and it is ringed by a substantial bank of earth and stone some 7 metres wide and standing between 1.3 and 1.5 metres high. Beyond that inner bank lies a fosse, the term for the encircling ditch that was dug to provide both material for the bank and an additional obstacle to entry, running 6 metres wide and dropping to 1.3 metres deep. Further out still is a second, lower outer bank, 5.5 metres wide and 0.7 metres high, giving the whole structure a notably layered, concentric profile. That outer bank has not survived uniformly; it disappears entirely along the north-western to north-eastern arc, whether through later agricultural disturbance or natural erosion it is not possible to say. A gap of 6 metres in the inner bank on the eastern side is likely the original entrance, the point through which people, animals, and goods once passed in and out.