During the 18th century the baptisms, marriages and burials were maintained in separate pages or registers. In the early years it was normal to only record the father's full name and that of his child for baptismal entries, therefore making it very difficult to search records. With each province headed by an Archbishop. Under them were 22 bishops, each in charge of a diocese. The boundaries of the diocese have remained constant and are used by both the Roman Catholic and Anglican churches.
Diocese boundaries have no relation to county boundaries, however.
Both Erenagh and Co-arb functions go back long before the introduction of Catholicism to Ireland, and are parts to the old Celtic religious organisation. Certain families were associated with particular parcels usually called termons. The Erenagh was appointed to his position by he Chief or Urragh, so the position wasn't hereditary per se, although it often was so in practice. The herenach was expected to maintain the Church buildings in his termon and support the Bishop and clergy from the proceeds of the land. He was therefore a territorial ruler of sorts.