Waterford city had the highest percentage of births outside marriage in the third quarter of 2011, according to the latest Vital Statistics figures from the Central Statistics Office (CSO).
The figures showed that 50 per cent of all births in the third quarter of 2011 in Waterford City were to unmarried parents, with 24 per cent of births being to unmarried parents living at the same address.
Limerick city came next.
In the same quarter, 46 per cent of births in Limerick City were outside marriage, with 16 per cent of all births being to unmarried parents living at the same address.
In Dublin city, 45 per cent of births were outside marriage and 18 per cent were to unmarried parents living together.
The lowest percentage of births outside marriage was in Co Roscommon at 22 per cent.
Overall, the third quarter figures show that 19,222 births took place, and 34 per cent of the total took place outside marriage. Eighteen per cent of all births nationally were to unmarried parents living at the same address.
The birth total in the third quarter of 2011 is 23 per cent higher than in 2002 when 15,593 babies were registered.
The 19,222 births represent an annual birth rate of 16.8 per 1,000 of the population.
The average age of mothers at maternity outside of marriage, was 28.4 years.
This ranged from 30.4 years in Dun Laoghaire Rathdown to 26.8 years in Limerick City.
The number of marriages registered during the quarter was 7,538, equivalent to an annual marriage rate of 6.6 per 1,000 population, a decrease of 0.4 compared with the corresponding quarter of 2010.