Greencastle
- County:
- Putnam County
- County Seat:
- Yes
- Area (mi²):
- 5.212
- State:
- Indiana
Greencastle is a city located in Putnam County, Indiana. Greencastle has a 2026 population of 9,907. It is also the county seat of Putnam County. Greencastle is currently growing at a rate of 0.07% annually and its population has increased by 0.9% since the most recent census, which recorded a population of 9,819 in 2020.