The average age of the population has gone up by over two years since 2011.
The CSO has figures from the Census last year.
Ireland's population is over 5.1 million for the first time in over 170 years - going back to the times of the Great Hunger.
That was what it was measured at in April last year - an 8% increase on 2016.
While the average age has gone up to 38.8 - there was a drop in the number of people who say they're in good health.
And the proportion of Catholics has fallen from 79% seven years ago to 69% now.