That detail alone gives the place a slightly puzzling quality. The walls, roughly a metre thick and built in what the Ordnance Survey memorably called the Cyclopean style, meaning large irregular blocks laid without fine dressing, were compared at the time to the great stone forts, or cahers, of the Aran Islands. It is an odd comparison for a building in low-lying north Kerry, sitting on what was effectively a promontory or island within a tidal estuary, hemmed by marshy ground on two sides and open to the elements on all others.

The church is thought to preserve the name of a saint called Mochua, whose feast day falls on 6 October according to the Félire Óengusso, a ninth-century martyrology written in Old Irish verse. That text places his church at Doire Mochua on the banks of the River Fial, now the Feale, which gives the site an early medieval devotional context even if the standing fabric is later in date. By 1302, the church appears in papal taxation records for the Diocese of Ardfert under the name De Fyngo, valued at 6 shillings and 8 pence per annum. In 1615, a Royal Visitation of the same diocese noted the parish of Dericoe being held by one Mr Stoughton in connection with Rattoo Abbey, with its value recorded at 25 shillings. Local tradition holds that the site was once an early monastic settlement, though nothing structural survives to confirm it.

The east gable remains the most complete part of the ruin, with a narrow round-headed window, splayed inward in the manner typical of early medieval Irish churches, its dressed sandstone surround still legible beneath considerable ivy growth. Flanking this window on the interior are two square-headed recesses, and a third sits in the south-east corner of the nave, positioned where a piscina, a small stone basin used for rinsing liturgical vessels, might be expected. Whether one is present there cannot be confirmed, as the oldest inscribed grave in the graveyard lies directly in front of it, blocking any investigation. The west wall has vanished entirely, and the bowed terminals of the surviving north and south walls are the result of later maintenance work rather than original construction.