What makes it worth a second look is what lies beneath its relatively recent foundation: the ground it occupies is thought to be a site of early Christian worship, one with connections reaching back considerably further than the building itself would suggest.

According to research compiled by Geraldine Stout and drawing on Appleyard's 1985 study of the area, the site is associated with St. Brendan of Clonfert, the sixth-century Irish monk better known for the extraordinary voyage narratives that bear his name. Brendan's connection to a site in Coolock Barony is not entirely surprising; early Irish saints were widely itinerant, and their names attached themselves to wells, churches, and plots of land across the country, often preserving a memory of monastic or devotional activity that predates any surviving structure by centuries. The present church building dates from the mid-18th century, constructed during a period when the Church of Ireland was consolidating or rebuilding many of its parishes across the Dublin region, frequently on ground that had long carried religious significance.

Tonlegee itself sits within what is now a largely suburban part of north Dublin, and the church is not a well-signposted destination. Visitors approaching with an interest in the early medieval layers of the site will find that the 18th-century fabric dominates what is visible above ground; the older associations are a matter of record rather than of obvious physical remains. The surrounding Coolock area retains little of its earlier rural character, which makes the continuity of this particular site, from an early Christian foundation through to a standing Georgian-era church, all the more quietly striking to those who know what to look for.