Elphin was the traditional site of a monastic house established by St Patrick c.435, although there are no remains of that date. It is believed to be one of the first monasteries founded by him. In pre-Reformation times, Elphin was a religious centre of international significance. This is supported by the appearance of Elphin in a number of pan-European maps in the Middle Ages. A pre-historic standing stone and St Patrick’s well are both situated within the Fair Green which forms part of the entrance into the Cathedral site.
The Diocese of Elphin was established in the year 1118, and her first Cathedral was dedicated to Beatae Mariae Virgini (Blessed Mary the Virgin). By the late 15th / early 16th century it was home to at least eighteen religious houses. However great changes were to follow, and the diocese lost many monasteries, convents and its Cathedral after the Cromwellian Conquest of Ireland.
A new Church of Ireland bishop's palace was built north of this site in 1749. Elphin's St. Mary's cathedral was also rebuilt in the eighteenth century. It was a modest building no bigger than a small parish church with a tall square clock tower at its west end. It was badly damaged in a storm in 1957 and was demolished a few years later, but its was partially restored in 1982 and the ruins can still be visited.