Ottawa
- County:
- LaSalle County
- County Seat:
- Yes
- Area (mi²):
- 14.895
- State:
- Illinois
Ottawa is a city located in LaSalle County, Illinois. Ottawa has a 2026 population of 18,775. It is also the county seat of LaSalle County. Ottawa is currently growing at a rate of 0.18% annually but its population has decreased by -0.24% since the most recent census, which recorded a population of 18,821 in 2020.