Towcester is an affluent market town and civil parish in the West Northamptonshire unitary authority area of Northamptonshire, England. From 1974 to 2021, it was the administrative centre of the South Northamptonshire district. Towcester is one of the oldest continuously inhabited settlements in the country. It was the Roman town of Lactodurum, located on Watling Street, today’s A5. In Saxon times, this was the frontier between the kingdom of Wessex and the Danelaw.