The name Killybegs is often associated with St. Cronan of Cill Beg or Kilbeg. We find Cronan Cille Bicci, in the Martyrology of Tallagh, at the 21st of February. A short distance from Prosperous is a townland bearing the same name. Here, there is an old ruined church, the quadrangular nave of which is alone tolerably perfect yet, the side-walls, north and south are much injured. In the end-wall is a beautiful mullioned two-ope window of small size.
The two extreme gables yet stand, and from one to the other, the measurement interiorly is 62 feet 6 inches. The nave in width was 18 feet 4 inches and the walls were about 2 feet 8 inches in thickness. Within a high oval breastwork fence the old graveyard is considerably elevated above the surrounding levels, generally a mark of remote antiquity, especially in rural districts.