Plainfield
- County:
- Brule County
- County Seat:
- No
- Area (mi²):
- 35.472
- State:
- South Dakota
Plainfield is located in Brule County, South Dakota. Plainfield has a 2025 population of 32 . Plainfield is currently declining at a rate of -3.03% annually and its population has decreased by -3.03% since the most recent census, which recorded a population of 33 in 2020.
The median age in Plainfield is 45.5 years: 38.5 years for males, and 45.5 years for females. For every 100 females there are 146.7 males.