The church comprises a chancel (w. c.8.00 m ), mainly 13thc. and an aisleless 15thc. nave. Of the original conventual buildings the sacristy, adjoining chamber and the W wall of the E range survive. There is a sealed chamber on the far S of the E range which is also 13thc. Part of the original 13thc. cloister arcading survives, but most is a replacement of c.1860 from a restoration led by Sir Benjamin Lee Guinness. Most other surviving features are 15thc. or later.

The chancel has a number of surviving, plain 13thc. features including the rebuilt N and S windows and the triple E window. There is also a round-headed 13thc. sedilia in the S wall of the chancel. This has bulbous bases with a chamfered torus below nook-shafts. Simple capitals support the arch, which has a filleted angle roll, front and rear, with a pointed moulding on the soffit. The label has a raised, central keeled roll on the angle, flanked by a smaller roll. There is an aumbry in the E end of the S wall, of two chamfered orders.

On the S side of the chancel is a plain round-headed (not ashlar) S doorway leading into the sacristy. This has an open stone stairway (modern) leading to an upper floor. The entrance to the upper chamber is round-headed of one chamfered order with a chamfered label and there is a plain round-headed window in the upper S wall. The upper parts of the building are restored.

The sacristy has a S doorway leading to a chamber with a barrel-vaulted roof and a plain round headed window, restored on the exterior. The exterior S doorway to this chamber is round-headed with a chamfered, restored label with acanthus label stops. The chamber abuts onto a smaller chamber on the W, which is only accesible via the cloister.

Romanesque sculpture is found on the reset N doorway, and on the doorways and windows of the E range.

An Early Irish Monastery was founded at Cong in 624, and St Feichin is said to have been the Abbot. Cong was chosen as one of the five bishoprics of Connaught at the Synod of Rathbreasail in 1111 but was not acknowledged at the Synod of Kells (1152).(Gwynne and Hadcock 1971, 166)

The Annals of the Four Masters record that the abbey was raided and burned in 1114 and 1137. Toirdhelbhach Ua Conchobhair (Turlough O'Connor) refounded Cong as an Augustinian Abbey in c.1134.

In 1203 the Annals of Loch Ce record that the town and monastery were completely destroyed by William de Burgo. Rebuilding was probably funded by the O Dubthaigh (O'Duffy) family (Leask 1941, 108).

Ruaidri Ua Conchobhair retired to Cong in 1183 and died there in 1198, although he was buried at Clonmacnoise. Several of his children were buried at Cong.

Leask notes that the abbey church, which he dates to c.1226 (Leask 1960, 59), may have originally had a N transept or aisle, but acknowledges that there is no evidence for this. He estimates that the nave and chancel would have been c. c.36.58m in length (Leask 1941, 109).

The reset N doorway appears to be the earliest surviving feature at Cong. Leask suggests that the jambs of the doorway could be of 15thc. date, but it seems more likely that they are unfinished, and were intended to be carved with palmettes. He dates the doorway to no earlier than 1200. Killanin and Duignan report that the N doorway was reset in 1860, having been moved from a point further W in the N wall. They suggest that it may originally have been a S processional doorway opening into the cloister.

As with all School of the West sites there are numerous comparisons and parallels to be made with other sites. Leask points out affinities between shallow-carved foliage at Cong and Annaghdown (Galway) and remarks on its classical character. (Leask 1941, 109) He also draws comparisons with foliage carving at Boyle. Stalley has pointed out a strong resemblance between the foliage carving on a label stop on the sedilia at Corcumroe and the label stop of one of the Chapter House windows at Cong. (Stalley 1975, 43)

Stalley has suggested that the 'Ballintober Master', thought to be responsible for the carving at Ballintober and Boyle, also worked on the doorways in the E range at Cong (Stalley 1987, 187). The chevron in the fourth order slype doorway is parallelled at Ballintober and a number of the capitals of the doorways in the E range may be compared with similar ones at Boyle (Kalkreuter 2001, 102-103, 106-107; Stalley 1973, 1830) The interior second order R capital of the Chapter House doorway is similar to a capital with palmette and berry carving at Boyle, but is far more like capitals on the reset N doorway. The first order capitals of the Chapter House doorway, are similar to a capital in the nave at Boyle.

Leask sees the influence of Ballintober in a plain three-order doorway in the E range of the cloister. This doorway leads into a small chamber which backs onto a barrel-vaulted chamber on the E (there is no doorway between the chambers). The doorway and this arrangement are paralleled at Ballintober.

Leask dates the doorways in the E range to be between 1200-1220 and suggests that a French sculptor may have been responsible for some of the designs. Stalley also suggests a date no later than 1220 for the doorways in the E range (Stalley 1973, 1830). Kalkreuter suggests a date 'after the first two decades of the 13thc.' (Kalkreuter 2001, 106)

The 19thc. restorations at Cong are generally the work of a local mason, Peter Foy, employed by Sir Benjamin Lee Guinness in 1860 (Killanin and Duignan 1967, 179). Foy also worked on the Cloister arcade.