St. Clair County, Illinois: Power, Data Centers and the Local Economy
Home to Belleville, St. Clair Township and Caseyville Township
St. Clair County hosts some of the generating capacity Illinois runs on. St. Clair County is home to Belleville, St. Clair Township, Caseyville Township and O'Fallon. 155 MW of new generation is planned here across 2 units, led by Geronimo Power (solar). 155 MW of it is already under construction or built. Next door, St. Louis County, Missouri, has 7 data centers and 648 MW of planned generation. Its power plants have 1,821 MW of capacity, 97% of it coal, the 8th largest fleet in Illinois. 37 MW of that came online in 2019 or later, mostly solar.
Cities and towns in St. Clair County
St. Clair County is home to Belleville, St. Clair Township, Caseyville Township and O'Fallon.
And 16 smaller places.
- Collinsville also extends into Madison County.
Unincorporated communities (governed by the county): Darmstadt, Floraville, Paderborn, Rentchler, Scott AFB.
Residents are 2025 Census estimates for the part of each city, town or township inside this county. Census publishes no annual estimate for unincorporated communities.
What changed in St. Clair County
1st = the most. Ranks cover counties with a value on record.
| Measure | Then | Now | Change | Rank in Illinois |
|---|---|---|---|---|
| Population (2020 → 2025) | 257,057 | 250,708 | ▼ 2.5% | 9th of 102 by size |
| Total jobs (2019 → 2025) | 92,156 | 89,192 | ▼ 3.2% | 66th of 102 by growth |
| Average annual pay (2019 → 2025) | $44,618 | $59,034 | ▲ 32.3% | — |
| Electrical contractor jobs (2019 → 2025) | 296 | 318 | ▲ 7.4% | — |
| Unemployment rate (2019 → August 2026) | 4.4% | 3.9% | ▼ 0.5pts | — |
| Generating capacity added since 2019 | — | 37 MW | — | |
| Generating capacity retired since 2019 | — | 0 MW | — | |
| Planned generation (Aug 2026) | — | 155 MW | 9% of today's fleet | 15th of 57 by size |
Electrical contractors employ 318, up 7.4% since 2019 against up 3.9% statewide, at an average $104,791 a year. Employers here counted 89,192 jobs in 2025, down 3.2% from 2019. Unemployment was 3.9% in August 2026, against 4.4% in 2019. Ameren Illinois Company is the largest utility serving St. Clair County, one of 9 with territory here. Its residential customers paid an average 15.26¢/kWh in 2024. 250,708 people live here, down 2.5% since 2020, 9th of 102 Illinois counties by population.
Who powers St. Clair County
Net change in operating capacity since 2019: +37 MW. Colors follow the fuel legend above.
Utilities with service territory in St. Clair County
| Utility | Ownership | Service | Residential customers (systemwide) | Residential price, 2024 | Commercial share of sales |
|---|---|---|---|---|---|
| Ameren Illinois Company | Investor Owned | Bundled | 1,060,894 | 15.26¢ | 28% |
| Southwestern Electric Coop Inc - (IL) | Cooperative | Bundled | 24,822 | 13.68¢ | 17% |
| Tri-County Electric Coop, Inc (IL) | Cooperative | Bundled | 16,197 | 16.04¢ | 9% |
| Egyptian Electric Coop Assn | Cooperative | Bundled | 13,707 | 15.53¢ | 42% |
| Clinton County Elec Coop, Inc | — | — | — | — | — |
| Village of Freeburg - (IL) | — | — | — | — | — |
| City of Highland | — | — | — | — | — |
| City of Mascoutah - (IL) | — | — | — | — | — |
Customer counts, prices and sales shares cover each utility's whole system in the state, not only this county. Commercial sales include data centers.
Operating power plants 15
| Technology | Capacity | Share |
|---|---|---|
| Coal | 1,766 MW | 97% |
| Solar | 37 MW | 2% |
| Petroleum | 16 MW | 1% |
| Natural gas | 2 MW | 0% |
| Largest plants | Owner | Technology | MW | Since |
|---|---|---|---|---|
| Prairie State Generating Station | Prairie State Generating Co LLC | Coal | 1,766 MW | 2012 |
| Freeburg | Village of Freeburg - (IL) | Petroleum | 16 MW | 1948 |
| AES Belleville Solar LLC | AES Distributed Energy | Solar | 10 MW | 2021 |
| South Belleville Solar, LLC | Dimension Energy LLC | Solar | 5 MW | 2025 |
| St. Clair Solar 5 | Pivot Energy | Solar | 5 MW | 2025 |
| Millstadt IL 1, LLC | SRC Partnership 16, LLC | Solar | 2 MW | 2025 |
Planned generation 2
| Plant | Technology | MW | Status | Year | Owner |
|---|---|---|---|---|---|
| Bee Hollow Solar, LLC | Solar Photovoltaic | 150 MW | Under construction (>50%) | 2026 | Geronimo Power |
| SV CSG East St Louis | Solar Photovoltaic | 5 MW | Under construction (≤50%) | 2026 | SV CSG East St Louis LLC |
The St. Clair County labor market
| Industry (2025) | Jobs | Average pay | Concentration vs U.S. |
|---|---|---|---|
| All industries | 89,192 | $59,034 | 1.00 |
| Electrical contractors | 318 | $104,791 | 0.49 |
| Power and communication line construction | 27 | $57,286 | 0.19 |
Concentration is the BLS location quotient: 1.0 means the industry holds the same share of local jobs as it does nationally. Industry rows count private employers; cells BLS suppresses are left out.
Data centers and local rules in St. Clair County
No data center, local measure or delayed project is on record in St. Clair County. Illinois has 28 local measures on record statewide.
St. Clair County and its neighbors
Of the 7 counties that border St. Clair County, St. Louis County carries the most build-out activity: data centers, planned generation and operating plants combined.
| County | Population | Jobs since 2019 | Operating MW | Planned MW | Data centers | Local measures |
|---|---|---|---|---|---|---|
| St. Clair County | 250,708 | ▼ 3.2% | 1,821 MW | 155 MW | — | — |
| Clinton County | 37,128 | ▲ 2.6% | 47 MW | 53 MW | — | — |
| Madison County | 263,110 | ▲ 5.9% | 701 MW | 8 MW | — | — |
| Monroe County | 34,840 | ▲ 1.4% | 38 MW | — | — | — |
| Randolph County | 29,921 | ▼ 9.4% | 1,504 MW | — | — | — |
| St. Louis (city) MO | 278,144 | ▼ 4.0% | — | — | 14 | — |
| St. Louis County MO | 990,911 | ▼ 3.4% | 34 MW | 648 MW | 7 | — |
| Washington County | 13,564 | ▼ 6.6% | 5 MW | — | — | — |
More of Illinois
St. Clair County, answered from the record
Who provides electricity in St. Clair County, Illinois?
9 utilities have service territory in St. Clair County in the EIA-861 2024 report: Ameren Illinois Company, Southwestern Electric Coop Inc - (IL), Tri-County Electric Coop, Inc (IL), Egyptian Electric Coop Assn. The largest, Ameren Illinois Company, charged residential customers 15.26¢/kWh on average in 2024.
What county is Belleville, IL in?
Belleville is in St. Clair County, Illinois. About 40,237 people live there (2025 Census estimate).
What county is St. Clair Township, IL in?
St. Clair Township is in St. Clair County, Illinois. About 35,372 people live there (2025 Census estimate).
What county is Caseyville Township, IL in?
Caseyville Township is in St. Clair County, Illinois. About 34,825 people live there (2025 Census estimate).
What power plants are in St. Clair County?
15 operating plants with 1,821 MW of capacity. The largest is Prairie State Generating Station (1,766 MW, coal).
How much new power is planned in St. Clair County?
155 MW across 2 units in the August 2026 EIA-860M inventory, 155 MW of it under construction or built. The largest owner is Geronimo Power.
Are there data centers in St. Clair County?
The SAVRN Data Center Map has no data center in St. Clair County. The nearest activity on record is next door in St. Louis County.
Is St. Clair County adding jobs?
Employers counted 89,192 jobs in 2025 against 92,156 in 2019 (-3.2%, BLS QCEW).
Does St. Clair County have a data center moratorium?
No county-level measure is on record for St. Clair County. Illinois has 28 local measures statewide, listed on the state page.