What looks like an ordinary field boundary along its northern side is in fact the inner bank of a much older oval enclosure, one that predates the modern church by many centuries and still wraps around the site in a faint but traceable arc. The enclosure is bivallate, meaning it has two concentric banks with a ditch between them, a form commonly associated with early ecclesiastical settlements in Ireland. The outer bank and its external fosse, a shallow drainage or boundary ditch, survive only on the northern side, but their dimensions are still measurable: the bank runs about three metres wide and the fosse nearly five metres across, all of it worn down to a fraction of its original height yet still readable in the landscape.

The site has been identified with Derrylossary church, which was granted by the Archbishop of Dublin to the prebend of the Chancellor of St Patrick's Cathedral, Dublin. That grant places it within the medieval ecclesiastical structures that radiated outward from Dublin, tying even remote parish churches into the administration of the cathedral chapter. No trace of the original church survives above ground; the modern building and its walled graveyard have replaced whatever stood here before. What do survive, and what make this site genuinely unusual, are the bullaun stones. Bullauns are boulders or slabs with one or more cup-shaped hollows ground into them, found across Ireland at early Christian sites and occasionally at prehistoric ones; their precise function remains debated, though they are frequently associated with religious or ritual use. There are three granite examples within the enclosure at Ballinacorbeg, one inside the graveyard wall, one just outside it to the west, and a third about fifteen metres to the northeast. A fourth stone, noted by Price and Stephens in 1948 at roughly 200 metres northwest of the church, was relocated by archaeologist Chris Corlett in 2005, giving the site a small cluster of these enigmatic objects that would be remarkable anywhere, let alone concentrated around a single former church site in County Wicklow.