Almost three in four babies in Knowsley, Merseyside, are born outside marriage or a civil partnership - the highest proportion in the UK.
Blaenau Gwent in Wales and Blackpool are other areas topping the list for children born to unmarried parents, according to figures from the Office for National Statistics (ONS).
Harrow in London has the lowest rate in the country, with roughly one in five born outside marriage.
The average for the whole of the UK is 48%.
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.
Knowsley holds the top spot with 74.8% of babies, followed in second place by Blaenau Gwent (73.2%).
Blackpool (72.2%) and Hartlepool (70.4%) are next, with Merthyr Tydfil and Redcar & Cleveland 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 born outside marriage.
After Harrow (20.3%), the next lowest is the City of London (23.3%) followed by Westminster (25.3%).
Separate figures on teenage pregnancies show that Barrow-in-Furness in Cumbria has the highest rate in the UK, with roughly 17 in every 1,000 girls under 18 giving birth last year.
Wokingham in Berkshire and Epping Forest in Essex have the joint lowest rate of just over one in 1,000.
Here are the full figures for the areas with the 10 highest and lowest percentages of live births outside marriage or civil partnership:
Highest:
1. Knowsley: 74.8%
2. Blaenau Gwent: 73.2%
3. Blackpool: 72.2%
4. Hartlepool: 70.4%
5. Merthyr Tydfil: 70%
= Redcar and Cleveland: 70%
7. North East Lincolnshire: 69.1%
8. Hull: 69%
9. Halton: 67.4%
10. Barnsley: 67.2%
Lowest:
1. Harrow: 20.3%
2. City of London: 23.2%
3. Westminster: 25.3%
4. Kensington and Chelsea: 25.4%
5. Magherafelt, N Ireland: 26.5%
6. East Renfrewshire: 26.6%
7. Redbridge: 27%
8. Barnet: 27.4%
9. St Albans: 27.5%
10. Wandsworth: 27.5%