The suffragan sees of the Province are: The Archdiocese extend from Achill Island in the West to Moore parish on the River Shannon, a distance of 193 km (120 mi), and it the largest in the country.

Geographically split north/south by the two lakes, Loughs Mask and Corrib, Tuam has pastoral charge of the largest Gaeltacht area in Ireland and of six island parishes.

Shrule parish, now part of Galway diocese, is nestled in the Tuam geographical area in the east of Lough Corrib.

A partial rectification took place in 1890 when Galway exchanged Killannin parish for parts of Carraroe.

Following an Act of Parliament of 1833, the See of the established church was merged with that of the Diocese of Killala and Achonry.

The pre-Reformation diocese at various moments absorbed other local episcopal sees deriving from Celtic monastic jurisdictions.

Ireland's political scene and ecclesiastical was changed permanently by the coming of the Normans and the influence of the English Crown.

Additionally, the Penal Laws sought to curb or altogether extinguish the practice of the Roman Catholic religion amongst the majority population of the Archdiocese.

In 1825, Archbishop Kelly testified before a House of Commons Committee of enquiry that out of 107 places of worship in the diocese, only eighteen had slated roofs.

The others, he said, were thatched and wretched, insufficient to contain the congregations, and in many instances the public prayers were celebrated in the open air.

As persecution abated, and as priests became more plentiful, a new confidence grew and the small thatched buildings were superseded by more solid, ample structures.

In nine rural areas were proselytism was a problem, he had the Third order of St. Francis of Assisi provide schools, but, on the whole, primary education was patchy.

In the 20th century, however, Tuam diocese, under Archbishop Walsh, was to the fore in the provision of secondary schools, especially in the twenty-year period before 1967, when the State made building grants and free post-primary education available.

Ballintubber Abbey, County Mayo, founded in 1216, is unique in that it is the oldest medieval parish church in Ireland still in use.