At the eastern edge of Ballymore Eustace, a graveyard holds the quiet remnants of a medieval church whose history stretches considerably further back than any written record can confirm. Two high crosses and a cross slab survive in the burial ground alongside the ruin, and their presence points to an early Christian ecclesiastical site of some significance, one that was already well established long before the Normans arrived in Ireland.

The first documentary mention of a church here comes from 1192, but by 1227 it had already been attached to St. Patrick's Cathedral in Dublin as a prebend, meaning it formed part of the income assigned to a cathedral clergyman. At that point it was valued at 20 marks, a modest but meaningful sum. By the early sixteenth century it carried the name 'church of Blessed Mary of Ballymore', as recorded in a document dating to 1529 to 1534. A Royal Visitation in 1615 found it in good repair, though Archbishop Bulkley's visitation just fifteen years later told a different story, describing a structure already in decline. What remains today is fragmentary: two wall sections, one to the east standing around three metres high and containing a splayed ope, the other to the south barely reaching a metre, both incorporated into or abutting the 19th-century church that now occupies the site.

A stone font kept in the porch of the later church is thought to have originated in the medieval building. A second font sits in the graveyard itself, though its journey here was rather different; it is said to have come from the church at Coghlanstown, some distance away, making this modest graveyard an unlikely repository for the salvaged fragments of more than one vanished place of worship.