The walls have collapsed so thoroughly that none of the original architectural features remain, and the building's precise age can only be estimated. What the dimensions suggest, though, is a structure of some substance: more than eleven metres long and over six metres wide, oriented roughly west-north-west to east-south-east in the manner common to medieval Irish churches.

The date of construction is uncertain, though the building is considered probably medieval in origin. What makes the site quietly arresting is something subtler than the ruin itself. Faint traces of a curving scarp, a low earthen bank or scarped edge running to the south-east, south, and west of the church, hint that this may have been an early ecclesiastical enclosure. Such enclosures, roughly circular or oval in plan, are associated with some of the oldest Christian foundations in Ireland, often predating the Norman period and the more formalised church architecture that followed it. If the traces at Kilcallin do reflect an early enclosure, the site may have a longer history of religious use than the medieval masonry alone would indicate. The location was noted by Killanin in 1947, suggesting at least some antiquarian interest in the site in the mid-twentieth century, though detailed investigation does not appear to have followed.