According to Census 2016 data released yesterday, 481,388 people stated they had no religion - compared to 204,151 in 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).
The data corresponds with figures from Kilkenny County Council earlier this year indicating the Travelling Community here has grown substantially in recent years.
There were more male (637) than female (598) Travellers.
Meanwhile, the report also shows there were 977 Irish Travellers enumerated in the county in April 2016, unchanged from 2011. This was an increase of 296 (39.3%) on the number in 2011 (753).
There were more male (502) than female (475) Travellers in Meath and nearly half (49.9 per cent) of all Travellers in the county were aged under 20, compared to 31.9 per cent of the county's overall population.
The next largest grouping - "Any Other White background" accounted for 17,508 persons (9 per cent), an increase of 1,668.
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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 average overall age of members was 40.3 years, almost three years above the average for the general population.
The number of people to declare no religion, including atheists/agnostics, increased by more than 70 per cent between 2011 and 2016.
They now make up 10% of the population, making them the second largest category in the breakdown of affiliations under the "Religion" heading in the Census.
The Central Statistics Office (CSO) noted that there had been "significant increases" in the 25 years between 1991 and 2016 in the non-Catholic population, driven not only by growing numbers of people with no religion but by increases in other faiths. Their average age was 37.9 years, making the nearly two years younger on average than the county's population overall.
The 3,845 Church of Ireland members made up 2.4% of Tipperary's population. On average, Church of Ireland members in Leitrim were 5.3 years older (45.1 years) than the overall population in the county. Muslims (1,265 ) and Orthodox (633 ) completed the top five.
Here is a summary of some of the headline results from Census 2016 for County Longford, together with comparisons for Leinster and the State.