Under the Normans the town lost some of its importance and was a town of about a thousand inhabitants. By 1250 Dorchester had a thriving wool industry and was a busy market town, holding three weekly markets and three annual fairs, which was unusual because fairs usually only happened once a year.
In the thirteenth century the Franciscan Friars came to Dorchester.
The church ran the only available hospitals in the area, one of which was dedicated to St. John where the monks did their best to care for the poor.
In 1567 Dorchester had its first grammar school. Dorchester grew quite slowly and the population was certain to have been affected by outbreaks of the plague in 1563, 1579 and 1595.