According to Census 2016 data released yesterday, 481,388 people stated they had no religion - compared to 204,151 in 2011.
In the 2016 Census, 3,729,115 people marked themselves as Catholic - down 132,220 since 2011.
While Tuam (737) and Longford (730) led the way, Dundalk had the fifth highest proportion of Irish Travellers in 2016 after Navan (664) and Mullingar (571). Over half of all Travellers in the county were aged under 20, compared to fewer than 3 in 10 (28.7%) of the county's overall population.
The data also showed that the Irish Traveller population had grown by just over 5% from 29,495 in 2011 to 30,987 previous year.
This was an increase of 80 (6.9%) on the number in 2011 (1,155).
More than 3.7 million Catholics made up just over 78.3 per cent of the population in April past year, compared with 84.2 per cent in 2011 - a drop of 132,220.
By contrast, Drogheda had 152 Travellers, comprising 73 males and 79 females.
In April 2016, those who indicated a "White Irish" ethnic or cultural background amounted to 110,637 people (86.3% of the county's population), a decline of 1,649 on 2011. The next largest grouping - "Any Other White background" accounted for 4,841 persons (11.8%), an increase of 580.
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Over one in three of those with African ethnicity (38.6%) were born in Ireland (22,331 persons), along with 31.3% (2,126) of those with other Black backgrounds.
The 19,447 persons with a Chinese ethnic/cultural background made up 0.4% of the usually resident population, while persons of mixed backgrounds (70,603) constituted 1.5%.
In relation to "Religion / No religion", the report finds that Catholicism remains the predominant religion, accounting for 87.1% (138,968) of Tipperary's population in April 2016. However, this was down from 27,394 persons five years previously.
The average age of Muslims in Ireland is 26, compared with a state average of 37.4.
As with the State overall, the next largest group was those with no religion.
Kilkenny County Council has said the increase is not attributable to people moving in from neighbouring counties, but rather due to the young age at which couples are starting families.
The Church of Ireland has the third-highest membership, with 126,414 people.
However, the Church of Ireland, with 126,414 members at last year's census, experienced a 2% decrease.