This is a cillín, the Irish term for an informal burial ground used for those whom the Catholic Church would not permit in consecrated soil, most often unbaptised infants. The stones at Treanmanagh are modest, standing only around forty to fifty centimetres high, and several have fallen. They are not memorials in any conventional sense; they mark presences without identifying them.

According to local tradition, unbaptised babies and children up to the age of fourteen were buried here during the eighteenth and nineteenth centuries. When O'Sullivan and Sheehan documented the site in 1996, it was heavily overgrown and appeared to be little more than a poorly preserved semicircular cairn of small stones, roughly six metres long and less than a metre high. By 2000, clearance work had changed the picture considerably. With the overgrowth removed, kerbstones emerged delineating an oval area measuring approximately eight metres east to west and six metres north to south. The clearance also brought to light a cross-slab in the north-east corner of the burial ground, a carved stone that had gone unrecorded in the earlier survey. Mature trees line the western perimeter, and immediately to the north sits a separate cairn of stones, tentatively identified as a penitential cairn, with two mature trees growing from it. Penitential cairns are associated with acts of devotional penance, often the ritual circling of a sacred site while reciting prayers, and their presence near places of marginal burial is not unusual in the Irish landscape.