Plainfield township
- County:
- Brule County
- County Seat:
- No
- Area (mi²):
- 35.472
- State:
- South Dakota
Plainfield township is located in Brule County, South Dakota. Plainfield township has a 2026 population of 32. Plainfield township 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.