
Seneca
- County:
- LaSalle County
- County Seat:
- No
- Area (mi²):
- 6.205
- State:
- Illinois
Seneca is a village located in LaSalle County, Illinois. Seneca has a 2025 population of 2,289. Seneca is currently declining at a rate of -0.48% annually and its population has decreased by -2.3% since the most recent census, which recorded a population of 2,343 in 2020.
The average household income in Seneca is $116,204 with a poverty rate of 19.37%. The median age in Seneca is 35.2 years: 34.7 years for males, and 35.7 years for females.