A baby boom and a high level of immigration have lifted the population to more than four million, its highest since 1871, according to the Central Statistics Office.
There are now 4.04 million people living in the Republic, compared with 4.05 million in the 26 southern counties in 1871.
The population increased by almost 65,000 in the past year, due to an increasing birth rate and immigration. The CSO estimates that 62,000 babies were born last year, and 50,100 immigrants came here. When deaths and emigration are taken into account, the population increased by 64,900, or 1.6 per cent.
Immigration, while high by historical standards, has fallen for the second year running. The 50,100 who came last year compare with 66,900 two years ago.
Just over one-third of the immigrants were Irish people returning. Thirty-six per cent came from the pre-enlargement EU and the US, with 30 per cent from the rest of the world. The largest single group of immigrants other than returning Irish, 12 per cent of the total, came from the UK. The next-largest was the Chinese, at 9 per cent.
The survey also showed a continued growth in the concentration of population on the eastern seaboard, with the mid-eastern region growing by 2.9 per cent, while the mid-western region grew by only 1 per cent.
Rising population partly reflects growth in the economy, with separate CSO figures yesterday confirming that employment is continuing to increase. The number at work rose by 48,200 in the past year to 1.836 million. This meant that the number of people at work was more than 45 per cent of the population, a record level in recent history. The construction and services sectors are booming, but employment in hotels and restaurants is falling, and many areas of manufacturing industry remain under pressure.
Adjusting for normal seasonal trends, the figures show that total job numbers continued to increase into the second quarter of this year.
The most rapid jobs growth has been in the Border, Midlands and Western region, although this is being driven in part by the rapid growth of long-distance commuting to work in Dublin from counties such as Louth.
The CSO figures show a small increase in the unemployment rate to 4.6 per cent, although long-term unemployment continues to fall.