Collinsville
- County:
- Madison County
- County Seat:
- No
- Area (mi²):
- 15.438
- State:
- Illinois
Collinsville is a city located in Madison County, Illinois. Collinsville has a 2026 population of 23,766. Collinsville is currently declining at a rate of -0.48% annually and its population has decreased by -2.47% since the most recent census, which recorded a population of 24,368 in 2020.