The population has increased by 34 thousand over the last year, bringing the total to more than 5 million.
It’s the first time it’s passed that mark since the 1851 census, just after the Famine.
New CSO figures show more births than deaths in the year to April – and just over 65 thousand immigrants, with 54 thousand emigrants.
The number of Irish nationals returning over the last year is the highest since 2007.