There were 65,909 babies born in Ireland last year, according to new figures released by the Central Statistics Office (CSO).
There were 1,300 more boys than girls delivered, while last year's total figure marks a drop of more than 1,500 births on 2014.
The average age of mothers was 32.5 years, while almost two in five births were for first time mothers whose average age was 30.7 years.
36% of births in 2015 were outside marriage, while a majority of those were to cohabiting parents.
The HSE's Sexual Health and Crisis Pregnancy Programme has welcomed the decline in the number of births to teenagers - which dropped from 1,253 in 2014 to 1,187 last year.
Orla McGowan, Education Officer with the programme, said: “The Relationships and Sexuality Education (RSE) Programme in schools and in youth centres has had a significant contribution to the figures released today.
"Parents and guardians also have a huge influence on their teenagers and while some teenagers might try to shut down a conversation about relationships and sex, it is important that they know the facts before they decide to have sex for the first time," she added.
Jack and Emily were the most popular names for babies in 2015 yet again - Jack having been the most popular boys' name every year since 2007, and Emily for girls in each of the last five consecutive years.
Other CSO statistics released today show there were 29,952 deaths registered in 2015.
The figures include 205 infant deaths - meaning an infant mortality rate of 3.1 deaths per 1,000 live births.
Meanwhile, 22,116 marriages were registered in 2015 - 91 of which were same-sex marriages.
