More than two thirds of babies in Hartlepool are born outside marriage or a civil partnership, which is among the highest in the UK.
The new figures show the town has 70.4% babies born outside marriage or a civil partnership, the highest in the North East and fourth in the UK.
The average for the whole of the UK is 48%, according to the Office for National Statistics (ONS).
The ONS figures show that areas with the highest proportion of babies born outside marriage or civil partnerships tend to be in the north of England and Wales.
The highest rate is in Knowsley, Merseyside, with 74.8% of babies, followed in second place by Blaenau Gwent (73.2%).
Blackpool (72.2%) and Hartlepool (70.4%) are third and fourth, with Merthyr Tydfil and Redcar & Cleveland coming in at joint fifth on 70%.
Hastings in East Sussex has the highest percentage in the south of England (65.6%).
By contrast, London has seven of the 10 areas with the smallest percentage of babies being born outside marriage.
Harrow in London has the lowest rate in the country, with roughly one in five born outside marriage.
After Harrow (20.3%), the next lowest is the City of London (23.3%) followed by Westminster (25.3%).