St. Clair County GIS Maps
St. Clair County, Illinois, has 257,400 residents and covers 657.7 square miles. The population declined 4.7% between the 2010 and 2020 census. More residents left than arrived over that decade. The FIPS code for St. Clair County is 17163.
Belleville is the county's largest population center. St. Clair County also includes 27 zip codes, 12 public school districts and 46 municipalities. Those boundaries help explain why population, schools, and housing can look different from one part of the county to another. The map below shows how those county lines, zip codes, and school districts fit together, and the sections that follow use that same geography to show population, demographics, school enrollment and housing patterns in more detail.
Maps, GIS layers and sample data. Paid packages add full layers, analytics and database files.
St. Clair County Trends
- Population
- 257,400▾
- Median Home Value
- $168,800▴
- K-12 Enrollment
- 25,258▴
County analytics dashboards with historical trends & projections included in package downloads.
Free starter access previews county maps, lightweight GIS, and sample data. Paid packages unlock full GIS layers, analytics, and database files.
St. Clair County Maps
The maps below show a few of the county map styles included in our downloads. County packages include map exports in JPEG, PNG, SVG, PDF and GeoTIFF formats plus more than 20 GIS layers for mapping, research and analysis. Available layers include zip codes, area codes, subdivisions, school districts, political boundaries, roads, water features, points of interest and more.
County packages also include historical county demographics, business intelligence, analytical dashboards, AI-ready prompts, markdown files and related reference data. Everything is organized to save hours of manual work collecting current data, cleaning it and joining it together. That makes it easier to move faster on analytics, due diligence, business planning and location research. Paid packages are built for commercial use, but some package contents include source-specific attribution or notice guidance. Review Licensing & Data Source Notices.
St. Clair County Population
St. Clair County had 257,400 residents in 2020. That was 4.7% lower than in 2010. St. Clair County added 1,318 people between 2000 and 2020, which points to steady long-term growth. The county is fairly spread out, with about 391 people per square mile. Some of the county's most populated postal areas include O Fallon, Belleville and Belleville.
Population Trend in St. Clair County IL
St. Clair County Population per 2000, 2010 and 2020 census counts with a baseline 2030 projection.
St. Clair County Zip Codes
St. Clair County has 27 zip codes. Some of the county's most populated zip codes include O Fallon (62269), Belleville (62226) and Belleville (62221). O Fallon is the largest zip by population, with about 36,068 residents or 14% of the county total. Together, the three largest zips account for about 37% of all county residents based on 2020 population estimates.
Most Populated Zip Codes in St. Clair County IL
| ZIP | Area | Population | Trend |
|---|---|---|---|
| 62269 | O Fallon | 36,068 | ▴ 15.1% |
| 62226 | Belleville | 29,156 | ▾ -2% |
| 62221 | Belleville | 29,039 | ▴ 4.2% |
| 62220 | Belleville | 19,474 | ▾ -5% |
| 62208 | Fairview Heights | 16,992 | ▾ -2.2% |
| Download all zip code data | |||
St. Clair County Zip Code populations and trends per most recent census data.
St. Clair County Demographics
St. Clair County has a median age of 39.5, which makes the county a little older than Illinois overall. About 23.3% of residents are under 18, while 16.8% are 65 or older. That gives the county a fairly even mix of younger families and older adults. The largest age group is 25 to 44 at about 31.9% of the population, which points to a solid working-age base. About 30.7% of adults have a bachelor's degree or higher, above the statewide figure of 37.2%. The county is majority White by population, with Hispanic, Asian, Black and multiracial residents making up a meaningful share of the local mix.
Key Demographics for St. Clair County IL
Median Age
39.5
Under 18
23.3%
Age 65+
16.8%
Bachelor's+
30.7%
St. Clair County School Districts
St. Clair County is served by 12 public school districts with 25,258 students enrolled in 2024. The largest districts on the county map are Collinsville Community Unit 10, East St. Louis 189 and Mascoutah Community Unit 19. Those three districts account for about 59% of public school enrollment in the map area. Total enrollment has stayed fairly steady in recent years, but it is slightly lower than it was in 2017.
Largest School Districts by Enrollment in St. Clair County IL
| District | Enrollment | Share | Trend |
|---|---|---|---|
| Collinsville Community Unit School District 10 | 6,031 | 23.9% | ▴ 1.1% |
| East St. Louis School District 189 | 4,646 | 18.4% | ▴ 0.2% |
| Mascoutah Community Unit School District 19 | 4,345 | 17.2% | ▴ 3.3% |
| Cahokia Community Unit School District 187 | 2,991 | 11.8% | ▾ -2.1% |
| Waterloo Community Unit School District 5 | 2,767 | 11% | ▴ 0.9% |
| Download all school district data | |||
St. Clair County school district enrollment and trends per most recent NCES reporting data.
St. Clair County Housing & Real Estate
St. Clair County has a median home value of $168,800 and a median gross rent of $1,032. About 68% of occupied homes in the county are owner-occupied, so the local housing market leans heavily toward ownership. Home values run below the Illinois median, while rents come in below the state average. In March 2026, the median listing price was $194,000 and homes spent about 49 days on the market.
St. Clair County Housing Mix
St. Clair County housing mix: owner, renter and vacant units.
St. Clair County Housing Trends
St. Clair County median home value and rent trend (last 5 years).
Businesses in St. Clair County, IL
St. Clair County has 9,526 business listings across 822 categories. The largest categories in St. Clair County business listings are Churches & Religious Organizations (346, 3.6%), Insurance Agencies (134, 1.4%), and Auto Repair (124, 1.3%). The full St. Clair County business listings dataset includes names, categories, addresses and contact details where available. St. Clair County packages also include U.S. Census County Business Patterns data with establishment counts, employment and payroll by industry sector.
Top Business Categories in St. Clair County, IL
| Category | Businesses | Share |
|---|---|---|
| Churches & Religious Organizations | 346 | 3.6% |
| Insurance Agencies | 134 | 1.4% |
| Auto Repair | 124 | 1.3% |
| Beauty Salons | 115 | 1.2% |
| Fast Food | 114 | 1.2% |
| Contractors | 106 | 1.1% |
| Community & Nonprofits | 104 | 1.1% |
| Gas Stations | 103 | 1.1% |
| Real Estate Agents | 102 | 1.1% |
| Parks & Recreation | 100 | 1.0% |
St. Clair County Business Listings
| Business | Category | City |
|---|---|---|
| Gateway Foundation | Abuse And Addiction Treatment | Caseyville |
| Southwestern Illinois College Bookstore | Academic Bookstore | Belleville |
| Villas at Crystal Lake | Accommodation | Swansea |
| Krener Bookkeeping & Tax | Accountant | Mascoutah |
| St Clair County Anglers | Active Life | Millstadt |
| SuZen Acupuncture | Acupuncture | O'Fallon |
| Bottoms Up | Adult Entertainment | Brooklyn |
| Knockerball618 | Adventure Sports Center | Fairview Heights |
| The Fource Group | Advertising Agency | O'Fallon |
| Sexy Fox Foods | African Restaurant | Fairview Heights |
| Download St. Clair County business listings | ||
St. Clair County business listings sourced from Overture Maps. Includes locations with a high level of confidence.
Get the Full St. Clair County Data Package
This page shows a preview of what's included in the St. Clair County data package. The full package gives you a ready-to-use county data system with GIS layers, historical data, maps, database files and planning tools that save hours of manual data gathering, cleanup and joins. Everything is organized to help you skip data wrangling and start analysis faster.
- 20+ GIS layers for zip codes, school districts, roads, water, boundaries and more
- Historical county demographics, housing, income and trend data
- ZIP code population files and school district enrollment history
- Database files, markdowns, AI-ready prompts and documentation
- Map exports in PNG, JPEG, PDF, SVG and GeoTIFF formats
- Offline-ready data explorer, map and analytics tools
Paid packages support commercial use, client work, and derived outputs. Some package contents may include source-specific attribution or provider notices. See Licensing & Data Source Notices.
One-time · instant download · 30-day refund guarantee · See full package details
Preview a Live Package Demo
See exactly what is included in a county data package. Inspect how files are organized, the interactive data explorer and how maps and analytics are laid out. The demo loads a real sample package from Illinois — explore the full structure before you buy.
No email or download required. Opens in a preview window on this page.
Nearby Counties
Browse county data pages for the counties that border St. Clair County. These nearby pages include the same mix of county maps, demographic summaries, school district context, housing trends and package links.