Ireland operates under two distinct constitutional frameworks. The Republic of Ireland separated church and state through a 1972 referendum that removed the special position of the Roman Catholic Church from Article 44 of the 1937 Constitution. Northern Ireland remains part of the United Kingdom, where the Church of England holds established status nationally, though Presbyterian and Catholic churches dominate religious affiliation in that territory. The 2016 census recorded 78.3 percent of Republic of Ireland residents identifying as Catholic, down from 84.2 percent in 2011. Northern Ireland's 2011 census showed 40.8 percent Catholic and 41.5 percent Protestant or other Christian denominations, the first time Catholic identification approached parity with Protestant in census records since partition in 1921.
Catholic practice structures remain visible across the Republic despite declining adherence. The Angelus bell broadcasts on RTÉ Radio 1 daily at noon and 6pm, a practice unchanged since 1950. Catholic primary schools operate approximately 90 percent of state-funded primary education in the Republic through a patron system where the church owns school property and appoints boards of management. The Education Act 1998 made religious instruction part of the characteristic spirit of these schools, with opt-out provisions for parents. Baptism certificates function as enrollment criteria in oversubscribed Catholic schools, though the government announced plans in 2018 to remove this requirement by 2024. As of 2022, the Department of Education had transferred patronage of 12 schools to multi-denominational bodies under a reconfiguration process that began in 2012.
Weekly Mass attendance collapsed across generations. The 1974 survey conducted by the Catholic Communications Institute recorded 91 percent weekly attendance among Catholics. The 2011 Association of Catholic Priests survey found 18 percent weekly attendance, with urban Dublin measuring 14 percent. The 2016 European Social Survey placed Republic of Ireland weekly religious service attendance at 35 percent, the fourth-highest in Europe after Poland, Portugal, and Italy. Church construction followed demographic expansion until the 1990s, leaving many rural parishes with buildings opened between 1960 and 1995 now serving congregations one-third their intended capacity. The Diocese of Limerick announced in 2021 that 20 of its 60 churches would close or merge by 2030 due to priest shortages and maintenance costs exceeding collections.
Secularization accelerated after institutional scandals documented between 1999 and 2014. The Commission to Inquire into Child Abuse, established in 1999, published the Ryan Report in 2009 detailing systematic physical and sexual abuse in Catholic-run industrial schools and reformatories from the 1930s through the 1990s. The Murphy Report in 2009 identified mishandling of clerical abuse allegations in the Dublin Archdiocese between 1975 and 2004. The Cloyne Report in 2011 found the Diocese of Cloyne did not implement the church's own 1996 child protection framework until 2008. The Taoiseach Enda Kenny's Dáil Éireann speech on July 20, 2011 described the Vatican's response to Cloyne findings as elitism and narcissism, the first direct government criticism of Rome by a sitting Irish premier since independence. Priest ordinations in Ireland dropped from 28 in 2010 to 3 in 2020 according to Maynooth Seminary records.
Marriage equality and abortion referendums demonstrated constitutional divergence from Catholic teaching. The Thirty-fourth Amendment of the Constitution Act 2015 passed with 62.1 percent support on May 22, 2015, making Ireland the first country to approve same-sex marriage by popular vote. The Thirty-sixth Amendment on May 25, 2018 repealed the Eighth Amendment's constitutional abortion ban with 66.4 percent approval. Turnout reached 64.1 percent, the highest referendum participation since the 1995 divorce vote. Rural constituencies that voted against divorce in 1995 supported abortion access in 2018, including Roscommon-South Leitrim at 59.4 percent yes. The Health (Regulation of Termination of Pregnancy) Act 2018 took effect January 1, 2019, permitting termination up to 12 weeks without restriction and later for fatal fetal abnormalities or risk to maternal health. The Health Service Executive recorded 6,666 terminations in 2019 and 6,577 in 2020, compared to 3,265 Irish residents who traveled to England and Wales for procedures in 2017 before legalization.
Protestant denominations concentrate in border counties and Dublin's affluent southside. The Church of Ireland, an Anglican communion member, claims approximately 126,400 adherents in the Republic per the 2016 census, representing 2.8 percent of the population. This body administers both Christ Church Cathedral and St. Patrick's Cathedral in Dublin, the latter housing the largest church organ in Ireland with 4,000 pipes installed in 1902. Presbyterian Church membership in the Republic numbered 24,600 in 2016, though the denomination claims 216,000 members in Northern Ireland according to its 2020 statistics. Methodists accounted for 6,800 members in the Republic. Religious Society of Friends maintains seven active meeting houses in Ireland, including one at Eustace Street in Dublin operating since 1692, though national membership declined to approximately 1,500 by 2016.
Orthodox Christianity expanded through immigration from Eastern Europe. The 2016 census recorded 62,187 Orthodox Christians in the Republic, a 129 percent increase from 2011. Romanian citizens comprised 29,186 residents in 2016, forming the largest Orthodox population. The Romanian Orthodox Church established a diocese in Ireland in 2008, operating from the Church of the Annunciation on Arbour Hill, Dublin, a former Presbyterian building purchased in 2015. Russian Orthodox services occur at the Church of the Nativity on Harold's Cross Road, opened in 2011. Greek Orthodox worship continues at the Church of the Annunciation on Arbour Place, acquired in 1997 after operating from a rented space since the 1970s.
Islam constitutes the Republic's third-largest religion after Christianity and irreligion. The 2016 census identified 63,443 Muslims, representing 1.3 percent of the population, compared to 49,204 in 2011. The Islamic Foundation of Ireland, registered in 1959, operated Ireland's first purpose-built mosque at South Circular Road, Dublin, opened in 1976 on land donated by the government. The Dublin Islamic Centre opened at Roebuck Road, Clonskeagh in 1996, serving approximately 3,500 weekly attendees according to center records. Cork's Noor-Ul-Islam Mosque began construction in 2018 on the North Ring Road after planning permission delays from 2002. Halal certification follows European Union regulation, with slaughter requiring stunning per S.I. No. 311/2009 unless performed for religious purposes under derogation Article 4.4, a provision the Department of Agriculture confirmed applies to licensed halal abattoirs.
Judaism maintains historical presence despite population decline. The 2016 census recorded 2,557 Jewish residents in the Republic, down from a 1946 peak of approximately 5,500. Dublin Hebrew Congregation operates the Adelaide Road Synagogue, opened in 1892, serving Orthodox practices. The Progressive Jewish Congregation established in 1946 meets at Leicester Avenue, Rathgar. Ireland's only Jewish primary school, Stratford National School in Rathgar, closed in 1999 after enrollment fell below viable numbers. Terenure College rugby club historically drew Jewish players from the nearby Rathgar and Terenure areas, though demographic shifts reduced this connection by the 1990s. The Irish Jewish Museum at Walworth Road, Portobello occupies a former synagogue opened in 1917 and converted to museum use in 1985 under historian Asher Benson's direction.