Illaunloughan, or Oileán Lócháin, lies in Portmagee Channel a short distance west-northwest of Portmagee village on the Iveragh peninsula. It is a place recorded in the Ordnance Survey Name Books as a burial ground for children and adult strangers, a designation that makes it unusual even among Ireland's many peripheral sacred islands.

The island's name is uncertain in its origins. One theory connects it to a saint called Lochán, partly on the basis that the Martyrology of Oengus, a ninth-century Irish martyrological text compiled around AD 800, mentions two figures of that name. A related ecclesiastical site called Killoughane (Cill Lócháin) exists at the eastern end of the Iveragh peninsula, which lends some weight to the saintly connection. A more prosaic alternative derives the name from a word meaning chaff. Whatever its origins, the island carried a functioning monastic settlement, the remains of which include an oratory, a leacht (a low commemorative cairn or altar associated with early Irish Christianity), a gable-shrine, a hut site, and a well. Around fifty upright stone slabs are distributed across the island, most concentrated in rows along its western side. Archaeological excavations carried out over four seasons between 1992 and 1995 covered approximately seventy per cent of the island's surface.

In more recent centuries the island served as a ceallúnach, a type of informal burial ground used in Ireland for unbaptised infants and others excluded from consecrated parish cemeteries. The infant burials found here were notably well preserved, typically marked with plain uninscribed headstones, and many had been placed in small timber boxes made from Scots Pine. These later graves were concentrated toward the western side of the island, occupying the same ground as the rows of earlier slabs, layering one era's sorrow quietly on top of another's.