40 per cent of babies, whose mothers live in the Shannonside region, were born outside marriage last year.
New figures also reveal the average age of a woman when she first gave birth.
Figures from the Central Statistics Office reveal 1,502 babies were born to mothers who live in the Shannonside region last year.
A total of 897 of the women were married at the time and 605 were not.
There were a total of 346 births by Leitrim mothers - with 42 per cent outside marriage.
There were 486 births by Longford mothers - with almost 43 per cent outside marriage.
There were 670 births by Roscommon mothers - with nearly 38 per cent outside marriage.
The average age of a first-time mother in Leitrim last year was almost 33, while it was 30 in Longford, and nearly 31 in Roscommon.
