Vermillion
- County:
- Clay County
- County Seat:
- No
- Area (mi²):
- 4.661
- State:
- South Dakota
Vermillion is a city located in Clay County, South Dakota. Vermillion has a 2026 population of 11,877. Vermillion is currently declining at a rate of -0.92% annually but its population has increased by 1.3% since the most recent census, which recorded a population of 11,725 in 2020.