Jefferson
- County:
- Union County
- County Seat:
- No
- Area (mi²):
- 47.679
- State:
- South Dakota
Jefferson is located in Union County, South Dakota. Jefferson has a 2025 population of 50 . Jefferson is currently declining at a rate of -1.96% annually and its population has decreased by -1.96% since the most recent census, which recorded a population of 51 in 2020.
The median age in Jefferson is 32.9 years: 32.9 years for males, and 39 years for females. For every 100 females there are 82.0 males.