What remains above ground is a slightly raised, roughly semicircular area, about fifty metres across east to west, defined by a low arc of earthen and stone bank. Part of that bank retains an external kerb of large stones, possibly added at a later date, and at the north-west it takes on a stepped profile. At the north-east, where the bank once continued, a post and wire fence marking a residential boundary has taken its place. The southern half is simply gone, buried beneath the R328. Local tradition holds that a souterrain, an underground stone-lined passage of the kind often associated with early medieval settlement, lies somewhere in the western half of the interior.

A rath is an earthen ringfort, typically a farmstead enclosed by a bank and ditch, built and occupied in Ireland roughly between the fifth and twelfth centuries AD. The Carrownlough example conforms to that pattern, though its precise age was unknown until infrastructure work provided an unlikely opportunity for investigation. During pipe-laying for the Lough Mask Regional Water Supply Scheme in 2001, archaeological monitoring of the trench exposed two cuts in section beneath the road, interpreted as the basal remains of the enclosing fosse on the southern side of the rath. Charcoal recovered from the base of one of those cuts was radiocarbon dated to between 780 and 1020 AD. The following year, road-widening along the same stretch allowed excavation of a narrow strip immediately north of the carriageway, where two further fosses came to light. The inner fosse had a V-shaped cut filled with alternating layers of stone and silt; the outer had vertical sides and a flat, southward-sloping base. A small shallow pit containing heat-reddened clay, charcoal, and burnt timber fragments was also found nearby. Recovered finds included a perforated stone bead, several worked lithics, and animal bones, a modest but telling collection from what was evidently a functioning early medieval enclosure.