The proportion of the population that is Catholic is at
its lowest since 1961, while that with no religion has increased by 400%
in the past 20 years.The numbers began falling in the 1960s and 1970s, accelerating in the 1980s. The data shows the numbers of Catholics have fallen in every diocese in the past five years.
However, its actual congregation, standing at 3.86m in 2011, is the highest since records began.
Conversely, in the 20 years between 1991 and 2011, the numbers of atheists, agnostics, and those with no religion increased more than four- fold to a high of 277,237 last year. This group included 14,769 primary school-aged children and 14,478 of secondary school age. There were 4,690 children aged under one year who had no religion.
The largest proportionate increase was in atheism, from 320 to 3,905.
Of the 3.8m Catholics in Ireland in 2011, 92% were Irish. Of the remaining 8%, the biggest cohort were Poles followed by British. Between them, they accounted for more than half of all non-Irish Catholics.
The census found that significant increases in the non-Catholic population in the past 20 years were influenced by increases in the religions of immigrants from Eastern Europe, Africa, and Asia.
The data also shows:
* Members of the Church of Ireland increased by 6.4% to 129,039;
* The Muslim population increased sharply in the past five years to 49,204;
* The number of Orthodox Christians has increased more than five- fold since 2006 to 45,223;
* The number of Hindus has shown a 10-fold increase since 1991 and stands at 10,688;
* Buddhists account for the largest proportion of "other religions" at 8,702.
David Quinn, founder of pro-religion think-tank The Iona Institute, said there was no way of knowing exactly what people mean when they say they belong to "no religion" without further study.
"While Census 2011 clearly shows the number of people living in Ireland who genuinely have no religion is increasing rapidly, we still have to treat the figures with a certain amount of caution. Not belonging to any particular religion is not the same as being irreligious," he said.
Mr Quinn pointed to a US study which found one in five Americans do not belong to any religion: "As the Pew Forum survey indicates, ticking the ‘no religion’ box can simply mean a person doesn’t belong to any particular religion, but it doesn’t necessarily mean they are purely secular in their thinking, let alone that they are atheists. The fact that half of this group in America say they are religious or spiritual shows this."