The fort at Lemgare sits just inside Co. Monaghan, but its eastern and southern edges lie within roughly thirty metres of the Co. Armagh line, the stream having been straightened at some point to serve as a practical boundary marker. That geographical detail alone gives the site an oddly liminal quality, as if whoever built here was deliberately choosing ground that sat at the edge of things.

The fort occupies an oval area on a rock outcrop, measuring roughly thirty-nine metres on its longer axis and twenty-six on its shorter. Its defences are a combination of engineered and natural elements, which is not unusual for this type of monument. Where the rock itself rises steeply enough, a natural cliff face on the west and north-west does the work of a wall; elsewhere, an earth and stone bank approximately three metres wide was constructed around the base and over the south-eastern ridge to complete the circuit. A scarp, that is an artificially steepened slope, runs along the south-west and west, reaching about 1.9 metres in height. There appear to be two gaps in the perimeter, one at the south-east and a narrower one at the south, and the southern opening, at around 2.7 metres wide at the base, is considered the more likely original entrance. Inside, sheltered between two exposures of bare rock, the earthen banks of a rectangular house site survive, measuring just under ten metres by just under six, though the north-eastern side has almost entirely eroded away.