Castor is a village and civil parish in the City of Peterborough unitary authority, about 4 miles (6.4 km) west of the city centre. The parish is part of the former Soke of Peterborough, which was considered part of Northamptonshire until 1888 and then Huntingdon and Peterborough from 1965 to 1974, when it became part of Cambridgeshire.