251,149 people (2024 Census estimate, −2.3% since 2020)
658 square miles of land · 382 people per square mile
“Highest” and “lowest” are just order, not grades: a high rank for poverty or hazard losses means more of it. Each figure's source is in its section below.
28 active community water systems list St. Clair County in the area they serve, reporting 254,500 people served in all (a system that crosses county lines counts its whole population).
| IL AMERICAN-EAST ST LOUIS surface water · private · IL1635040 | 131,368 served |
| O FALLON buys surface water · local government · IL1631100 | 46,603 served |
| CASEYVILLE buys surface water · local government · IL1630250 | 13,798 served |
| CAHOKIA HEIGHTS buys surface water · local government · IL1635000 | 12,528 served |
| MASCOUTAH buys surface water · local government · IL1630800 | 8,759 served |
| AMERICAN WATER OPER AND MAINTENANCE, LLC buys surface water · federal · IL1635237 | 6,779 served |
| LEBANON buys surface water · local government · IL1630650 | 4,714 served |
| FREEBURG buys surface water · local government · IL1630600 | 4,707 served |
Source: U.S. EPA Safe Drinking Water Information System (SDWIS), active community systems, . Look up any system's violations and test results with EPA's search using its ID.
About 447 people were held in St. Clair County's jail, in Vera's latest figure (2021), or 274 per 100,000 residents ages 15–64. In 2016 it was about 385.
Source: Vera Institute of Justice, Incarceration Trends (built from federal Bureau of Justice Statistics jail surveys). Counties without their own jail, or that share one, may show no figure.
27 school districts have their office in St. Clair County. School taxes are usually the largest part of a property tax bill.
Spent $113.1 million — $94.1 million to run schools, about $19,597 per student, plus $15.7 million on buildings and equipment. Money in: $45.4 million local (mostly property tax), $51.3 million state, $10.2 million federal. Long-term debt: $46.8 million.
Spent $144.6 million — $132.5 million to run schools, about $28,313 per student, plus $9.6 million on buildings and equipment. Money in: $11.8 million local (mostly property tax), $102.6 million state, $23.5 million federal. Long-term debt: $15.8 million.
Spent $66.4 million — $58.2 million to run schools, about $14,025 per student, plus $2.8 million on buildings and equipment. Money in: $19.6 million local (mostly property tax), $39.6 million state, $26.6 million federal. Long-term debt: $61.4 million.
Spent $52.2 million — $46 million to run schools, about $11,672 per student, plus $832,000 on buildings and equipment. Money in: $27.9 million local (mostly property tax), $23.1 million state, $4.9 million federal. Long-term debt: $26.4 million.
Spent $72.1 million — $65.6 million to run schools, about $19,365 per student, plus $3.3 million on buildings and equipment. Money in: $19.6 million local (mostly property tax), $44.3 million state, $12 million federal. Long-term debt: $26.2 million.
Spent $82.5 million — $76.1 million to run schools, about $24,664 per student, plus $2.7 million on buildings and equipment. Money in: $10.4 million local (mostly property tax), $56.9 million state, $24.5 million federal. Long-term debt: $52.6 million.
Spent $43.5 million — $38.9 million to run schools, about $15,425 per student, plus $2.7 million on buildings and equipment. Money in: $26.7 million local (mostly property tax), $18.5 million state, $4.2 million federal. Long-term debt: $23.2 million.
Spent $16.9 million — $15.2 million to run schools, about $13,027 per student, plus $352,000 on buildings and equipment. Money in: $7.2 million local (mostly property tax), $8.3 million state, $1.8 million federal.
And 19 more.
Source: U.S. Census Bureau, 2023 Annual Survey of School System Finances. Districts are listed by the county of their main office; some serve neighboring counties too.
Source: County Health Rankings & Roadmaps 2025 (University of Wisconsin Population Health Institute), which gathers federal data (CDC, Census, and others); measures cover different recent years. Blank lines aren't reported for small counties.
Overall risk: Relatively High compared with other U.S. counties. FEMA estimates natural hazards cost St. Clair County about $174.6 million a year on average in buildings, crops and lives. Ability to bounce back (community resilience): Relatively High; social vulnerability: Relatively Low.
Source: FEMA National Risk Index (December 2025), expected annual loss. Ratings compare counties nationwide; they're estimates, not predictions.
485 bridges in St. Clair County: 235 in good condition, 205 fair, and 45 poor (9.3%). “Poor” means a main part — the deck, the beams, or the supports — is rated 4 or lower on the federal 0–9 scale. It doesn't mean unsafe to drive; unsafe bridges are closed.
| I-55/64; US 40 PSC over TRRA · built 1966 | 113,200 vehicles a day |
| I-55/70;/64 over CSXRR NSRR TRRARR · built 1959 | 66,500 vehicles a day |
| FAI 255 over ILL 15 · built 1981 | 44,300 vehicles a day |
| I-255 over NSRR · built 1980 | 41,500 vehicles a day |
| FAI 255 over ILL 163 · built 1980 | 41,500 vehicles a day |
| I-55/70 & US 40 EB over DRAINAGE CANAL · built 1960 | 33,250 vehicles a day |
Source: Federal Highway Administration, National Bridge Inventory (2025 submission). Includes state, county and city bridges.
Federal grants paid for $228.1 million of work in St. Clair County in fiscal 2025, about $886 per resident — to the county, cities, schools, hospitals, nonprofits and others.
Source: USAspending.gov, grants by place of performance, fiscal 2025 (Oct. 2024 to Sept. 2025). Search it by county to see each award.
From Grants.gov: posted grants listing county governments as eligible, soonest deadline first; research-only and overseas programs left out; list updated 2026-10-13, refreshed weekly. 62 are open in all. Cities, towns, school districts and nonprofits have their own lists there.
Registration deadlines, early voting and polling places for Illinois are on the federal site vote.gov, which links to the state's official election office.
The budget, property tax rates, audits, local officials and offices for St. Clair County come from the county's own records, which we haven't gathered — not gathered, never hidden. See what a full county site looks like, or ask to have St. Clair County built: brayden.ozark@gmail.com.
More of Illinois: the state government and every county in Illinois.
Nearby counties: Monroe County (19 mi) · St. Louis city, MO (21 mi) · Madison County (25 mi) · Clinton County (29 mi) · Washington County (29 mi) · Randolph County (29 mi).