The predominant religion in Ireland is Christianity, with the largest church being the Roman Catholic Church. Ireland’s constitution states that the state may not endorse any particular religion and guarantees freedom of religion. In 2011, 84.2% of the population identified themselves as Roman Catholic, 2.6% less than 5 years earlier, although the number of Catholics increased by 179,889.
Other significant Protestant denominations are the Presbyterian Church in Ireland, followed by the Methodist Church in Ireland. The second largest Christian denomination, the Church of Ireland (Anglican), declined in membership for most of the twentieth century, but has more recently experienced an increase, as have other small Christian denominations. The country’s Hindu and Muslim populations have experienced significant growth in recent years, due chiefly to immigration. In the 2011 census, 269,811 people (5.9%) had no religion, with 3,905 and 3,521 people describing themselves as “atheist” and “agnostic” respectively. Those who did not state a religion numbered 72,914 (1.6%). Researchers debate the relative significance of secularisation as a general feature of Irish society, the interpretation of census results and the extent to which religious syncretism is becoming more widespread.
From Religion in the Republic of Ireland (Wikipedia; footnotes omitted)