Towcester is a 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.

West Northamptonshire is a unitary authority area covering part of the ceremonial county of Northamptonshire, England, created in 2021. By far the largest settlement in West Northamptonshire is the county town of Northampton. Its other significant towns are Daventry, Brackley and Towcester; the rest of the area is predominantly agricultural villages though it has many lakes and small woodlands and is passed through by the West Coast Main Line and the M1 and M40 motorways. The district includes the site of the Roman town of Bannaventa, and the grade I listed Althorp House and its estate.