Union township
- County:
- Day County
- County Seat:
- No
- Area (mi²):
- 35.59
- State:
- South Dakota
Union township is located in Day County, South Dakota. Union township has a 2026 population of 73. Union township is currently declining at a rate of -1.35% annually and its population has decreased by 0% since the most recent census, which recorded a population of 73 in 2020.
The median age in Union township is 70.1 years: 70.1 years for males, and 65.8 years for females. For every 100 females there are 223.5 males.