Williamson County, Illinois: Power, Data Centers and the Local Economy
Home to Marion, Herrin and Carterville
Williamson County is living through the turnover of the U.S. power fleet. Williamson County is home to Marion, Herrin, Carterville and Johnston City. 12 MW of new generation is planned here across 3 units, led by Dimension Energy LLC (solar). 12 MW of it is already under construction or built. 173 MW has retired here since 2019, including Marion (coal, 173 MW, 2020). Construction employs 1,080, up 9.8% since 2019. 17 MW of that came online in 2019 or later, mostly solar.
Cities and towns in Williamson County
Williamson County is home to Marion, Herrin, Carterville and Johnston City.
- Freeman Spur also extends into Franklin County.
- Stonefort also extends into Saline County.
Unincorporated communities (governed by the county): Blairsville, Crab Orchard, Whiteash.
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 Williamson County
1st = the most. Ranks cover counties with a value on record.
| Measure | Then | Now | Change | Rank in Illinois |
|---|---|---|---|---|
| Population (2020 → 2025) | 67,127 | 67,225 | ▲ 0.1% | 22nd of 102 by size |
| Total jobs (2019 → 2025) | 28,246 | 29,573 | ▲ 4.7% | 23rd of 102 by growth |
| Average annual pay (2019 → 2025) | $40,330 | $55,243 | ▲ 37.0% | — |
| Construction jobs (2019 → 2025) | 984 | 1,080 | ▲ 9.8% | 29th of 56 by growth |
| Unemployment rate (2019 → August 2026) | 4.2% | 3.6% | ▼ 0.6pts | — |
| Generating capacity added since 2019 | — | 17 MW | — | |
| Generating capacity retired since 2019 | — | 173 MW | — | |
| Planned generation (Aug 2026) | — | 12 MW | 5% of today's fleet | 34th of 57 by size |
Employers here counted 29,573 jobs in 2025, up 4.7% from 2019. Its power plants have 266 MW of capacity, 56% of it natural gas. Electrical contractors employ 61, at an average $78,135 a year. Unemployment was 3.6% in August 2026, against 4.2% in 2019. Ameren Illinois Company is the largest utility serving Williamson County, one of 4 with territory here. Its residential customers paid an average 15.26¢/kWh in 2024. 67,225 people live here, up 0.1% since 2020.
Who powers Williamson County
Net change in operating capacity since 2019: −156 MW. Colors follow the fuel legend above.
Utilities with service territory in Williamson 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% |
| Southeastern IL Elec Coop, Inc | Cooperative | Bundled | 22,731 | 14.47¢ | 12% |
| Egyptian Electric Coop Assn | Cooperative | Bundled | 13,707 | 15.53¢ | 42% |
| Southern Illinois Elec Coop | — | — | — | — | — |
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 9
| Technology | Capacity | Share |
|---|---|---|
| Natural gas | 150 MW | 56% |
| Coal | 99 MW | 37% |
| Solar | 17 MW | 6% |
| Largest plants | Owner | Technology | MW | Since |
|---|---|---|---|---|
| Marion | Southern Illinois Power Coop | Coal | 249 MW | 1963 |
| East Marion IL 1, LLC | SRC Partnership 16, LLC | Solar | 4 MW | 2025 |
| Clendenin A Community Solar, LLC CSG | Clendenin A Community Solar, LLC | Solar | 2 MW | 2021 |
| Hurricane Creek CSG | SPG IL Hurricane Creek Solar LLC | Solar | 2 MW | 2021 |
| Lukuc B Community Solar LLC CSG | Lukuc B Community Solar LLC | Solar | 2 MW | 2021 |
| SV CSG Barrass Farms II LL | SV CSG Barrass Farms II LLC | Solar | 2 MW | 2023 |
Planned generation 3
| Plant | Technology | MW | Status | Year | Owner |
|---|---|---|---|---|---|
| Spillertown CSG 1 LLC | Solar Photovoltaic | 5 MW | Under construction (>50%) | 2026 | Dimension Energy LLC |
| Spillertown CSG 2 LLC | Solar Photovoltaic | 5 MW | Under construction (>50%) | 2026 | Dimension Energy LLC |
| SV CSG Corbell | Solar Photovoltaic | 2 MW | Built, not yet operating | 2026 | SV CSG Corbell, LLC |
Retired since 2019
| Plant | Technology | MW | Year |
|---|---|---|---|
| Marion | Coal | 173 MW | 2020 |
The Williamson County labor market
| Industry (2025) | Jobs | Average pay | Concentration vs U.S. |
|---|---|---|---|
| All industries | 29,573 | $55,243 | 1.00 |
| Construction | 1,080 | $62,871 | 0.69 |
| Electrical contractors | 61 | $78,135 | 0.29 |
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 Williamson County
No data center, local measure or delayed project is on record in Williamson County. Illinois has 28 local measures on record statewide.
Williamson County and its neighbors
Of the 6 counties that border Williamson County, Jackson 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 |
|---|---|---|---|---|---|---|
| Williamson County | 67,225 | ▲ 4.7% | 266 MW | 12 MW | — | — |
| Franklin County | 36,916 | ▲ 0.6% | 2 MW | — | — | — |
| Jackson County | 52,501 | ▲ 11.0% | 10 MW | 101 MW | — | — |
| Johnson County | 13,363 | ▲ 17.2% | — | 36 MW | — | — |
| Pope County | 3,672 | ▼ 9.1% | — | — | — | — |
| Saline County | 22,772 | ▲ 7.0% | 270 MW | 4 MW | — | — |
| Union County | 16,656 | ▲ 3.5% | 2 MW | — | — | — |
More of Illinois
Williamson County, answered from the record
Who provides electricity in Williamson County, Illinois?
4 utilities have service territory in Williamson County in the EIA-861 2024 report: Ameren Illinois Company, Southeastern IL Elec Coop, Inc, Egyptian Electric Coop Assn, Southern Illinois Elec Coop. The largest, Ameren Illinois Company, charged residential customers 15.26¢/kWh on average in 2024.
What county is Marion, IL in?
Marion is in Williamson County, Illinois. About 17,148 people live there (2025 Census estimate).
What county is Herrin, IL in?
Herrin is in Williamson County, Illinois. About 12,268 people live there (2025 Census estimate).
What power plants are in Williamson County?
9 operating plants with 266 MW of capacity. The largest is Marion (249 MW, coal).
How much new power is planned in Williamson County?
12 MW across 3 units in the August 2026 EIA-860M inventory, 12 MW of it under construction or built. The largest owner is Dimension Energy LLC.
Are there data centers in Williamson County?
The SAVRN Data Center Map has no data center in Williamson County.
Is Williamson County adding jobs?
Employers counted 29,573 jobs in 2025 against 28,246 in 2019 (+4.7%, BLS QCEW). Construction went from 984 to 1,080.
Does Williamson County have a data center moratorium?
No county-level measure is on record for Williamson County. Illinois has 28 local measures statewide, listed on the state page.