From The Peopling of New York City
Roman Catholics
The religion of Irish immigrants was Roman Catholicism, although there were some Protestants. The Irish faced hardship and discrimination because they made up a small population of Roman Catholics in a sea of Protestant Americans. A growing Irish immigrant population by the end of the nineteenth century in New York City led to an increase in the power of the Roman Catholic Church. Irish men and women took over the Roman Catholic Archdiocese of New York by 1880. Many Irish weren’t religious in the sense that they didn’t attend church frequently, however they still identified with Catholicism as a part of heritage and tradition. The relationship between gender ratio and degree of adherence is interesting. Women were the main carriers of fervent religious practice roughly a century after the Great Potato Famine, a trend that Emmet Larkin coined as, "the Devotional Revolution." It appears that women upheld the Roman Catholic identity and passed it on as tradition to the successive generations. The growth of the church in New York City had been phenomenal since 1820, when there were but two churches to serve the city's Catholic population of approximately 30,000.
The Church encompassed every part of the Irish immigrants' lives. Religion infiltrated their education, politics, occupations, lifestyles, and traditions. It was a militant Church--a Church who fought not only for their souls but also for their human rights. [1]
Irish New Yorkers had a special affinity for the Church's politics. Because of the influence of the Catholic church, many Irish-Americans served as politicians in Tammany Hall, a famous political machine that dominated the politics of New York City during the late nineteenth to mid-twentieth century.[2] Irish men dominated the church, Irish women became nuns and served as teachers in parochial schools and as nurses in the church's hospitals. Their labors made Catholic institutional life possible in New York City. [3]