Just under one in five of all births in the last quarter of last year were to cohabiting couples, according to the 
latest CSO figures [1]. An additional 15pc were born to single mothers living alone meaning that 34pc of all births were outside of marriage.
Limerick city had the highest number of births outside marriage in the fourth quarter at 50pc and 42pc of these births were to cohabiting couples. But in the whole of last year, the figure for births outside marriage in Limerick city was 55pc.
In Cork city, 49 per cent of births in the fourth quarter were outside marriage, with 18pc of all births being to unmarried couples with the same address.
In Waterford city, 45pc of births were to unmarried couples, but 29pc of all births were to unmarried parents living at the same address, the highest such figure in the country. The area with the next highest rate of births to cohabiting couples was Co. Laois, with 25pc of all births there in the last quarter of 2010 to unmarried parents living at the same address.
The lowest percentage of births outside marriage was in Dun Laoghaire Rathdown, Cork County and Galway County, each at 25pc.
According to Census 2006, five percent of all children in the country were living with a cohabiting couple. The only Irish research on cohabiting couples (by B Halpin and C O’Donoghue) has shown that within seven years three-quarters of cohabiting couples have either separated or married.
Data from other countries shows that marriage, on average, provides children with far more stability than cohabitation. According to the British Millennium Cohort Study, only 35 per cent of British children born into a cohabiting union will live with both parents throughout their childhood, compared with 70 per cent born to married couples.
In addition, the average length in Britain of a marriage that ends in divorce is 11.5 years compared with just two years for a live-in relationship. Irish data also shows that only 25pc of cohabiting couples are still cohabiting after seven years.
According to Census 2006, there was 121,000 cohabiting couples in Ireland that year. Proportionately this is on a par with the rate of cohabitation in the UK. However, most cohabiting couples here do not have children.
The number of children who are raised by cohabiting couples varies greatly in Europe from five percent here, to 12.9pc in the UK, to 30.5pc in Sweden.