Some 4,690 babies were categorised as having no religion last year, an analysis of Census 2011 findings by the Central Statistics Office has found.

It noted a four-fold increase in the number of people who said they had no religion, were atheists or agnostics, since 1991. Some 277,237 people fell into this category last year. The group included 14,769 children of primary school age, and 14,478 of secondary school age.

The analysis of Census 2011 also found the proportion of the population who were Catholics reached its lowest point in 2011 at 84.2 per cent, but its congregation, at 3.86 million, was the highest since records began. This was explained by the number of Catholic immigrants living here.

Of the 3.8 million Catholics in this State last year, 8 per cent were non-Irish. Polish people were the biggest group with 110,410 Catholics, followed by the UK with 49,761.

Experts said that the growing numbers of atheists and large increases in the religions of immigrants from Eastern Europe, Africa and Asia led to the changes. Some 110,410 Poles account for the largest non-Irish group of Catholics.

The Iona Institute, which describes itself as a pro-marriage, pro-religion think tank, said the figures on non-religious should be assessed with caution.

“Not belonging to any particular religion is not the same as being irreligious,” spokesman for the organisation David Quinn said.

He pointed to a survey by the prestigious Pew Forum in the US that found that one in five Americans does not belong to a religion but half of this group consider themselves to be either religious or spiritual.

“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,” Mr Quinn said.

The CSO also noted a sharp increase in unemployment among Travellers – rising from almost 75 per cent in 2006 to more than 84 per cent last year.

There were 29,573 Travellers living here in April 2011, accounting for 0.6 per cent of the total population. Co Galway had the highest number of Travellers with 2,476 people, followed by south Dublin with 2,216. There were only 152 Travellers enumerated in Co Waterford.

Deirdre Cullen, senior statistician at the Central Statistics Office (CSO), said the latest Census 2011 report shows the growing diversity of the population.

“This report again underlines the fact that Ireland has an increasingly diverse population where changing cultures and religious beliefs play an important part,” she said.