Like most dioceses in Ireland the present Diocese of Clonfert had its origin in the Synod of Rathbreasail in 1110, reaching its final form at the Synod of Kells in 1152 when it was made a suffragan of Tuam. Before that the early Irish monastery and school of Clonfert was the dominant ecclesiastical centre in the area and an important centre of learning in the early Irish church; Cummian, an important theological writer was from there. It nestled close to the river Shannon on its western bank and its “paruchia” intermingled with that of Clonmacnois. Despite the vicissitudes of these early centuries its fame grew and the annals record, apart from bishops, abbots and coarbs of the founder, Brendan, the names of numbers of scribes, lectors, anchorites and “fir-leighin”, who laboured and prayed and studied there. It was also deeply involved in the eighth century spiritual reform movement of the “Céili Dé”.

In the early 13th century its bishop was one of those appointed by Honorius III to investigate a dispute over the election of the Bishop of Ardfert (Kerry); later in the century it was provided with a bishop of Italian birth — one of the very few occasions when this happened in Ireland — Bishop John was in Clonfert for many years until he was translated to become Archbishop of Benevento in the 1290s. Because of the quality of its land, a century later it was judged by Rome to be richer than its metropolitan see and ordered to pay 300 gold florins as the tax on the accession of a new bishop. Tuam had to pay only 200.

Saint Brendan’s fame as a sea-faring missionary contributed to its pre-eminence in later times and led to its choice as an episcopal see in the twelfth century. He was held in reverence from Brittany to the far-off Faroes. It must have been this established reputation that caused his name to be attached to the medieval tale, the “Voyage of Brendan”, which made its way into the literatures of Europe and led to later voyages of discovery.

Territorially, the modern diocese occupies almost the whole of East Galway, with one parish, Lusmagh in County Offaly and Taughmaconnell as well as Creagh, the half-parish of Ballinasloe in County Roscommon. This was the ancient territory of Hy Many, the largest petty-kingdom in the country, as it existed when the diocese was formed. In fact, its bishop was sometimes referred to as the Bishop of Hy Many.

Clonfert Cathedral, the nave of which is twelfth century or earlier, still stands and its western doorway, supreme example of the Hiberno-Romanesque style, is on architectural grounds assigned a date of about 1180. The place had been burned in 1179. Before that one of the important events of the Twelfth Century Reform took place there. As the “Annals of Clonmacnois” described it: “In the year 1170 there was a great convocation of the clergy of Ireland at Clonfert by commission from the Pope for the reformation of certain abuses of a long time used in Ireland.” St. Laurence O’Toole presided there as Papal legate.

The diocese was divided into four deaneries, Clonfert, Loughrea, Urrachree and Duniry, having 15 rectories and 39 vicarages with a chapter and offices after the Norman pattern. Four houses of Canons Regular and four of Canonesses were established in the Irish deaneries.

Bishops of the diocese, in the 14th and 15th centuries introduced mendicant orders—Franciscans to Kilconnell, Kilnalahan and Meelick, with their 3rd Order to Clonkeenkerril and Kilbocht; Dominicans to Portumna, with their 3rd Order to Kilcorban and Carmelites to Loughrea. The Canons disappeared with the Reformation, but the Mendicants remained to become an important factor in maintaining religion during the Penal Times until, with the establishment of Maynooth College in 1795, the flow of secular priests became adequate again. Evading the law by registering as parish priests in 1704, they served one-third of the parishes throughout the eighteenth century.

Forty-one parishes in 1704 were by the year eighteen hundred amalgamated into twenty four, with little change to the present time. The chapter disappeared after Emancipation, when an era of church building began, which replaced the poor structures of the Penal Times and included such worthy churches as those at Ballymacward and Ballinasloe, the latter designed by McCarthy and Pugin. Landlord intransigence prevented the building of a cathedral in Loughrea until 1897 when Bishop Healy laid the foundation stone, which was fortunate because the era of the Celtic Revival and Irish Stained Glass had begun, with happy results in its interior decoration.

The Sisters of Mercy were brought to Loughrea in 1850 by Bishop Derry and spread to five towns in the diocese, operating primary and secondary schools, industrial schools at Loughrea and Ballinasloe and a domestic economy school at Portumna. They also staffed the workhouse hospitals in Loughrea, Ballinasloe and Portumna and latterly the county home in Loughrea. The Sisters of Mount Carmel, who have been in Loughrea since the 17th century, conducted a school there up to 1860 but have since been an enclosed order. In 1945 Bishop Dignan introduced the Franciscan Missionaries of the Divine Motherhood to Ballinasloe, where they built Portiuncula Hospital, which has been enlarged many times since and is now a general hospital under the Western Health Board.

The diocesan seminary, begun at Loughrea by Bishop Derry in the 19th century, was succeeded by St. Joseph’s College at Cartron, at Esker and finally at Garbally Park since 1924. The Dominicans, who had come from Athenry, ran a college at Esker for a time, where now the Redemptorists have a house for retreats.