The Population of England in the Middle Ages
After the Romans departed Germanic peoples, the Angles, Saxons and Jutes landed in England and they gradually conquered it. However many Celts survived and were assimilated into Saxon society. However the Saxons never gained effective control of Cornwall.
Another great wave of invasion came in the 9th century. The Danes conquered North and Eastern England. At that time England was divided into kingdoms and they only one left was the southern kingdom of Wessex led by Alfred the Great. Alfred eventually defeated the Danes and they made a treaty. They split southern and central England between them. The Danes took London, East Anglia and all the territory east of the old Roman road, Watling Street. Alfred took the land west of Watling Street and southern England. However in the 10th century Wessex gradually expanded and took over all the Danish territory. So a single united England was created. The Danish settlers were gradually assimilated into English society.
At the time of the Domesday Book (1086) England probably had a population of about 2 million. (Much less than in Roman times). However the population grew rapidly. It may have reached about 5 or 6 million by the end of the 13th century.
In the Middle Ages most people lived in the countryside and made a living from farming. However at the time of the Domesday Book (1086) about 10% of the population of England lived in towns. Moreover trade boomed in the following two centuries and many new towns were founded.
The first thing that would surprise us about those towns would be their small size. At the time of the Domesday Book in 1086 London had a population of about 18,000. By the 14th century it rose to about 45,000. Other towns were much smaller. York may have had a population of about 13,000 by 1400 but it then fell to about 10,000 by 1500. Most towns had between 2,000 and 5,000 inhabitants.
However disaster struck in 1348-49 when the Black Death reached England. It killed about 1/3 of the population. The plague returned again and again and the population of England was severely reduced. In 1400 the population of England was probably about 2 1/2 million.