In the 1650s, Catholics were uprooted from their productive, arable, lands in several Irish counties by Oliver Cromwell’s Protestant army and forced at musket point to desolate, barren, Connacht. Their confiscated lands, the better holdings in Ireland, were distributed to Protestant settlers, Cromwell’s army as pay, and carved up to pay debts. Maps of Ireland, pre and post Cromwell, detailing the regression of the predominantly Catholic associated Irish language and customs point to a culture that was deliberately and officially forced to areas thought of as being so inhospitable they would not survive. County Mayo was included among these religious and cultural ghettoes. The living standards of the banished Catholics fell dangerously low and remained so for centuries. Christian duty led some within the Protestant clergy to later establish evangelical missions in the wild Irish west to give relief to the descendants of those very same Catholics. Salvation and, dishonourably, food were offered through conversion to Protestantism. Whereas 17th century Protestants believed it was God's will that godless Catholics be sent to suffer and perhaps perish in Mayo, 19th century Protestants believed it was His will that these (still godless ) Catholics be reclaimed so that they might be saved. The Rev Edward Nangle's Achill Island Mission set out to do just that in 1831.
The verve to proselytise was partly out of Protestant fear for their faith after the granting of Catholic emancipation by the British government in 1829. By 1850, eight Protestant clergymen were employed on Achill and five churches had been built. The role of the Church of Ireland as the state church ended in 1871. As a result of this and several additional factors, the Protestant population in the south of Ireland fell, slowly at first and then sharply after Irish independence. In 1891, there were 4,351 Protestants in Mayo. That figure had fallen by 1,000 by 1911 and had been more than halved by 1926. In 1981, the Church of Ireland population in Mayo stood at 984, out of a total county population of 114,766. Mayo had mirrored the general trend of declining Protestant numbers that was witnessed throughout the Republic. In the face of such demoralising patterns, the tiny Protestant population of Inishbiggle fought life and the elements to hold on to its reformed faith.
The Church of Ireland Holy Trinity Church on Inishbiggle was built about 1870 and provided service to more than 80 of that denomination at that time. Nangle's mission, only a few kilometres away on neighbouring Achill, had succeeded in getting converts on Inishbiggle. Ninety souls were living on the island in the early 1980s and four of them were Protestant. Bachelor James Gallagher (68 ), his sister Ellen Gallagher (72 ), his widowed sister Annie Sheperd (70 ) and her son Frank (30 ) made up the congregation. James was church warden of Holy Trinity Church which was still being used to host service every second Sunday. Clergymen holidaying at the old rectory on Achill would minister to the three churches in the parish at Achill Sound, Dugort, and Inishbiggle during the summer months. When rough weather would not allow crossings by currach, the duty of ministering was taken on by the retired Reverend Herbert Friess. Friess was a former Lutheran minister who had fled Nazi Germany in 1939. He had spent time as the Rector on Achill. When required on Inishbiggle, the septuagenarian would travel 20 kilometres from his retirement home to be ferried to the island where he would then walk the distance to Holy Trinity Church. In 2003, the church was blessed and re-dedicated to serve both the Protestant and Catholic communities on the island.