South Petherwin is a village and civil parish in east Cornwall, England, United Kingdom. It is in the Registration District of Launceston. The civil parish is bounded to the north by the Launceston parishes of St Thomas and St Mary Magdalene, to the east by Lawhitton and Lezant parishes and to the west by Trewen parish. The population of the parish in the 2001 census was 932. The district falls in the Altarnun electoral ward but the population of the civil parish at the 2011 Census was almost unchanged at 931.