These were places set apart, often at the margins of parishes, where unbaptised infants and others considered outside the rites of the institutional church were laid to rest. The Catholic Church historically denied such individuals burial in consecrated ground, and so communities created their own quiet places of interment, frequently at ancient earthworks, ruined churches, or field boundaries that carried a sense of long use and informal sanctity. The practice continued in some areas well into the twentieth century, and the sites remain, largely unmarked, in the landscape.

Cilliní are found across Ireland in their hundreds, perhaps thousands, and Mayo has a particular concentration of them. They speak to a grief that was once made to carry an extra burden, the exclusion of a dead child from the community's formal rites of mourning. Many of these sites are now difficult to identify on the ground without local knowledge, as they were deliberately kept separate from the official record of the parish. The land around Kilsallagh, with its Atlantic-facing terrain in the west of the county, would have been home to generations of farming families for whom such a place would have been quietly known and carefully maintained, even without markers or inscriptions that might survive today.