Eureka
- County:
- McPherson County
- County Seat:
- No
- Area (mi²):
- 34.308
- State:
- South Dakota
Eureka is located in McPherson County, South Dakota. Eureka has a 2025 population of 38 . Eureka is currently declining at a rate of -2.56% annually and its population has decreased by -5% since the most recent census, which recorded a population of 40 in 2020.
The median age in Eureka is 77.7 years: 0 years for males, and 0 years for females. For every 100 females there are 166.7 males.