The proportion of Catholics in the population fell from 84.2% to 78.3% in the same period.
There are 730 Irish Travellers living in Longford town, the second highest number among towns of a population of 1,500 or more persons.
Among females, just 13.3 per cent were educated to upper secondary level or above, compared to 69.1 per cent of the general population, while 57.2 per cent of males were educated to primary level at most, compared with just 13.6 per cent of the general population. Travellers made up less than 1 in 100 (0.8%) of the county's population, compared to 0.7% nationally. It's an increase of 73.6 percent in five years, making it the fastest growing "religion". It shows the number of Traveller families increased by 20% in the past year alone. Over half (52.6%) of all Travellers in the county were aged under 20, compared to just under 3 in 10 (29.7%) of the county's overall population.
Catholicism is still the dominant religion in Ireland as 3.7m people declared themselves as Catholics in this year's Census, down 3.4 percent since 2011.
As with the State overall, the next largest group was those with no religion.
In relation to "Ethnicity", those who indicated a "White Irish" ethnic or cultural background amounted to 139,178 people (87.4% of the county's population), a decline of 818 on 2011.
This was followed by persons with "Any other White background" (9.5%), non-Chinese Asian (1.7%) and "other including mixed background" (1.5%).
Over one in three of those with African ethnicity (38.6 percent) were born in Ireland (22,331 persons), along with 31.3 percent (2,126) of those with "other Black backgrounds". That's up from a figure of 157 families in 2015, while the figure was 170 families the two years previous. The average age of Catholics in the county was 40.6 years, slightly above the county's overall average age of 40.2 years.
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 2,631 Church of Ireland members in the county made up 2% of its total population.
Orthodox (1,690) and Muslims (949) completed the top five. On average, Church of Ireland members in Leitrim were 5.3 years older (45.1 years) than the overall population in the county. According to data, 481,388 people said they had no religion, compared with 204,151 in 2011.