St. Clair County IL United States
| County FIPS | 17163 |
| Largest City | Belleville |
| State | Illinois |
| Latitude | 38.4703 |
| Longitude | -89.9284 |
| Population | 253,694 |
| Density | 385.8 people per square mile |
| Time Zone | America/Chicago |
Median household: $73,854
Median individual: $40,542
Mode: 60.1% White
Median house value: $176,613.0
Median: 39.9 years old
With at least college degree: 31.8%
With STEM degree: 38.4%
Never married: 34.6%
Unemployed: 6.0%
All data comes from the SimpleMaps US Counties Database, 2026.
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