The total number of people with no religion increased more than 400% in the 20 years between 1991 and 2011.
According to the latest figures released by the Central Statistics Office about Census 2011, 277,237 of the population (6%) now describe themselves as having no religion, or being agnostic or atheist.
The number of people who describe themselves as Catholic is increasing but represents a smaller percentage of the total population.
The congregation is now 3.86m, the highest since records began.
However, it now represents 84% of the total population, reaching the lowest point since records began.
Among the non-Irish, Polish people represented the largest group, with 110,410 people, followed by people from the UK with 49,761.
According to today’s figures, the same period has also seen significant increases in the non-Catholic population.
There were 129,039 members of the Church of Ireland in April 2011, an increase of 6.4% on 2006.
There were 49,204 Muslims in Ireland in April 2011, a rise of 51.2%, making them the third largest religious group the country.
There were 45,223 Orthodox Christians in Ireland in April 2011, more than double the number five years earlier.
The total number of Irish Travellers in April 2011 was 29,573, accounting for just over 0.5% of the total population.
Among 15 to 29-year-olds, 33% were married, compared with just over 8.2% of the general population.
Just over a quarter of Traveller women had five or more children, compared with just 2.6% of women overall.
The number of Travellers who completed third level in 2011 was 115 (1%).
This compares with 30.7% of the rest of the population.
Unemployment in the Traveller community was 84.3% in 2011, up from 74.9% five years earlier.
Travellers had higher rates of disability than the general population.
In 2011, 17.5% of Travellers had one or more disabilities compared with 13% for the State as a whole.