A 15thc. building incorporating a late Romanesque E window and early Gothic N doorway. Loose fragments of early 13thc. date are found in the church, which is disused and roofless.

Traditionally granted to St Brendan of Clonfert by the king of Connacht who died in 578. Monastery burnt in 1142. First known bishop mentioned in 1189. Between 1252 and 1302 Annaghdown became an archdeaconry in the diocese of Tuam. In 1327 the diocese was united with Tuam.

The N door and E window were probably built for the first cathedral in the late 12thc. when Annaghdown became an Episcopal see. The keel moulding of the E window suggests a date of c.1200 or slightly later (Garton, 1981, 53-4). The rich decoration of the triangular panels and the inclusion of snakes and beasts in the chevron are similar to the S doorway at Killaloe Cathedral and to sculpture at Tuamgraney. The low relief foliage carving and the use of framed and continuous window mouldings relates to the 'School of the West'. The mouldings of the N doorway appear to be more advanced in date, perhaps contemporary with the loose stones (1220s?). The use of beasts as mouldings is similar to and possibly inspired by the E window. The decoration of the loose fragment (i) is similar to chevron on the E windows at Killone, Co. Clare.