Religious freedom is constitutionally provided for in Ireland. Christianity is the predominant religion, and while Ireland remains a predominantly Catholic country, the percentage of the population who identified as Catholic on the census has fallen sharply from 84.2 percent in the 2011 census to 78.3 percent in the most recent 2016 census. Other results from the 2016 census are : 4.2%  Protestant, 1.3% as Muslim, and 9.8% as having no religion. According to a Georgetown University study, before 2000 the country had one of the highest rates of regular Mass attendance in the Western world.While daily attendance was 13% in 2006, there was a reduction in weekly attendance from 81% in 1990 to 48% in 2006, although the decline was reported as stabilising. In 2011, it was reported that weekly Mass attendance in Dublin was just 18%, with it being even lower among younger generations.

Which group in Ireland from the 2016 census is larger: Catholic or Muslim?
Catholic