Onida
- County:
- Sully County
- County Seat:
- Yes
- Area (mi²):
- 0.672
- State:
- South Dakota
Onida is a city located in Sully County, South Dakota. Onida has a 2026 population of 644. It is also the county seat of Sully County. Onida is currently declining at a rate of -1.98% annually and its population has decreased by -3.45% since the most recent census, which recorded a population of 667 in 2020.
The median household income in Onida is $70,000 with a poverty rate of 4.85%. The median age in Onida is 42.2 years: 49.3 years for males, and 38.4 years for females. For every 100 females there are 104.4 males.