The Republic's population has passed 4 million for the first time since 1871. The latest figures from the Central Statistics Office reveal that the population last April was 3.98 million, up from 3.92 million in the census taken 12 months earlier.
But it has increased even further in the last eight months to over 4 million because the birth rate in Ireland now far exceeds death rates, according to the CSO.
The excess of births over deaths in the 12 months to April was 31,900, compared with 17,500 in 1995. That trend is expected to continue for the foreseeable future.
Net migration - the difference between the number of people moving to and from the State - has also added to the population since April.
The latest figures mean the Republic's population has increased by just over 1 million since 1971, when it was 2.98 million.
The population was 4.05 million in 1871, the last time it went above 4 million. The Republic's population is measured in a census every five years. In the intervening period the CSO compiles an annual estimated population figure by tracking births and deaths and migration trends.
Data is also compiled via continuous country of residence inquiries at airports and ports, the register of electors, the numbers of work visas granted and the number of asylum applications lodged.
The latest CSO data reveals immigration peaked in the 12 months to April 2002, when 66,900 people came to settle in Ireland. It fell to 50,500 in the 12 months to April 2003.
It is believed worsening economic conditions in recent years have slowed the rate of immigration. Changes have also been made to legislation governing the residency rights of parents of Irish-born children making Ireland a less attractive destination for many expectant parents.
Emigration was the lowest in the 12 months to April, at 20,700, since the CSO began compiling such data in 1987. Some 60 per of those who emigrated went to the US or EU member-states.
Just over one third of immigrants, 35 per cent, are Irish people returning to live here.
