The current official population of the island of Ireland is 6.4 million.
A census in the Republic and the North, carried out in 2011, have been combined for the first time.
The figures show that 4.6 million people live south of the border and 1.8 million live in Northern Ireland.
Since 2002 the population in Ireland has grown by 17%, two and a half times the rate of growth in the north of 6.9%.