Figures released by the Central Statistics Office in Dublin last week show that as of April this year, 4.04 million people were calling the Republic home.
It was the first time in 133 years that the population of the equivalent area on the island had topped the 4 million mark.
The Northern Ireland census returns in 2001 turned up a population of just under 1.7 million for the northern six counties
A combination of both census calculations, and allowing for natural increases during the tabulation period, would mean that the population of the entire island of Ireland is now in excess of 5.75 million souls.
The island was home to an estimated 8.5 million at the outbreak of the Famine in 1845 but declined sharply in succeeding decades due to death, disease and mass emigration.
The population of the Republic’s 26 counties in 1871 was estimated at 4.05 million.
While the U.S. baby boom took off after World War II — demographers assign the phenomenon to the years 1946-64 — the Irish equivalent came somewhat later, in the 1970s.
This Irish boom followed an all-time low for the 26 county population in 1961. The census of that year revealed a population of just 2.8 million.
Despite dire predictions of further drops, the Republic’s population ticked upward from that low throughout the rest of 1960s, this despite continuing emigration.
As things currently stand, there are more births than deaths in the Republic and the resulting natural population increase is being augmented by inward migration.
2002 was a peak year for immigration, with almost 70,000 people arriving in Ireland from other countries. That number dropped to just over 50,000 arrivals in 2003.
The inward migration was initially fueled by Irish emigrants being drawn back to Ireland by the Celtic Tiger years of the mid- and late 1990s.
But returning Irish now make up only about a third of new arrivals, down from a high of roughly 50 percent a few years ago, according to Central Statistics Office calculations.
Roughly a third more of the new arrival total is entering Ireland from countries other than the U.S. and outside the European Union. Almost 10 percent of immigrants arriving in the Republic are now Chinese.
Emigration is currently at a significantly lower level than immigration. A total of 18,500 people departed the Republic’s shores last year. Most of them were under 25.
The U.S. and EU attracted about 60 percent of this total, with the remainder going to other countries, most notably Australia and New Zealand.