Surprise Valley
- County:
- Mellette County
- County Seat:
- No
- Area (mi²):
- 33.505
- State:
- South Dakota
Surprise Valley is located in Mellette County, South Dakota. Surprise Valley has a 2025 population of 15 . Surprise Valley is currently declining at a rate of 0% annually and its population has increased by 7.14% since the most recent census, which recorded a population of 14 in 2020.
The median age in Surprise Valley is 72.2 years: 0 years for males, and 0 years for females. For every 100 females there are 106.3 males.