Duncan
- County:
- Spartanburg County
- County Seat:
- No
- Area (mi²):
- 7.175
- State:
- South Carolina
Duncan is a town located in Spartanburg County, South Carolina. Duncan has a 2026 population of 4,594. Duncan is currently growing at a rate of 3.12% annually and its population has increased by 12.87% since the most recent census, which recorded a population of 4,070 in 2020.