More than 3.7 million Catholics made up just over 78.3% of the population in April 2016, compared to 84.2% in 2011 - a drop of 132,220.
Meanwhile the number of people to declare no religion, including atheists/agnostics, increased by more than 70% over the same five year period.
According to Census 2016 data released on Thursday 481,388 people stated they had no religion - compared to 204,151 in 2011.
This group made up 10.1% of the population, compared with 6% five years previously.
Other changes in the religious make-up of the country included a 28.9% increase in the number of Muslim residents.
The statistics showed there were 63,443 Muslims in Ireland in April 2016, up from 49,204 in 2011.
Almost half were living in Dublin city and suburbs.
There was also an increase in the numbers of Orthodox Christians and the Apostolic and Pentecostal population.
Members of the Church of Ireland decreased slightly as did the number of Presbyterians.
The data also showed that the Irish Traveller population had grown by just over 5% from 29,495 in 2011 to 30,987 last year.
Almost 60% of Travellers were aged under 25, compared with just 33.4% of the general population.
More than 30% of Travellers aged 15 to 29 were married, compared with 5.8% of the general population.
According to the report educational attainment among Travellers continues to lag significantly behind that of the general population and the vast majority - 80.2% - were unemployed.
In terms of ethnic composition White Irish remains the largest group, accounting for more than 80% of residents.
