These grounds are known in Irish as cillíní (singular: cillín), and they served for centuries as the designated resting places for infants who died unbaptised. Under Catholic theological doctrine as it was understood and practised in Ireland, an unbaptised child could not be buried in consecrated ground, and so communities established their own peripheral spaces, often on liminal ground such as island edges, old ringfort banks, or boundaries between townlands, where these children could be laid to rest.

The place name Illannaglashy suggests an island setting, the word "illan" or "oileán" being a common Irish element meaning island, and the location off the Mayo coast would fit the pattern of choosing marginal, in-between spaces for cillíní. The practice of using such sites continued in some parts of Ireland well into the twentieth century, long after its theological underpinnings had begun to soften. For families, these were not forgotten or shameful places; they were tended, known, and mourned over, even if they existed outside the formal structures of parish burial. The emotional geography of a cillín is often quietly visible in how a community speaks about it, or in the small unmarked stones that sometimes survive above ground.