Plattsmouth
- County:
- Cass County
- County Seat:
- Yes
- Area (mi²):
- 3.316
- State:
- Nebraska
Plattsmouth is a city located in Cass County, Nebraska. Plattsmouth has a 2026 population of 6,887. It is also the county seat of Cass County. Plattsmouth is currently growing at a rate of 1.1% annually and its population has increased by 4.4% since the most recent census, which recorded a population of 6,597 in 2020.