Jefferson County, Illinois: Power, Data Centers and the Local Economy
Home to Mount Vernon, Mount Vernon Township and Shiloh Township
Jefferson County is where a large share of Illinois's next power plants are planned. Jefferson County is home to Mount Vernon, Mount Vernon Township, Shiloh Township and Dodds Township. 155 MW of new generation is planned here across 2 units, led by RWE Clean Energy (solar). 155 MW of it is already under construction or built. 2 MW of that came online in 2019 or later, mostly solar. Its power plants have 2 MW of capacity, 100% of it solar. Employers here counted 19,432 jobs in 2025, down 2.4% from 2019.
Cities and towns in Jefferson County
Jefferson County is home to Mount Vernon, Mount Vernon Township, Shiloh Township and Dodds Township.
And 1 smaller places.
Unincorporated communities (governed by the county): Opdyke.
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 Jefferson County
1st = the most. Ranks cover counties with a value on record.
| Measure | Then | Now | Change | Rank in Illinois |
|---|---|---|---|---|
| Population (2020 → 2025) | 36,998 | 36,147 | ▼ 2.3% | 38th of 102 by size |
| Total jobs (2019 → 2025) | 19,915 | 19,432 | ▼ 2.4% | 62nd of 102 by growth |
| Average annual pay (2019 → 2025) | $44,016 | $59,848 | ▲ 36.0% | — |
| Unemployment rate (2019 → August 2026) | 4.5% | 4.6% | ▲ 0.1pts | — |
| Generating capacity added since 2019 | — | 2 MW | — | |
| Generating capacity retired since 2019 | — | 0 MW | — | |
| Planned generation (Aug 2026) | — | 155 MW | 7750% of today's fleet | 14th of 57 by size |
Ameren Illinois Company is the largest utility serving Jefferson County, one of 3 with territory here. Its residential customers paid an average 15.26¢/kWh in 2024. Unemployment was 4.6% in August 2026, against 4.5% in 2019. 36,147 people live here, down 2.3% since 2020.
Who powers Jefferson County
Net change in operating capacity since 2019: +2 MW. Colors follow the fuel legend above.
Utilities with service territory in Jefferson 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% |
| Tri-County Electric Coop, Inc (IL) | Cooperative | Bundled | 16,197 | 16.04¢ | 9% |
| Wayne-White Counties Elec Coop | Cooperative | Bundled | 11,957 | 16.58¢ | 21% |
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 1
| Technology | Capacity | Share |
|---|---|---|
| Solar | 2 MW | 100% |
| Largest plants | Owner | Technology | MW | Since |
|---|---|---|---|---|
| Marlow Solar, LLC CSG | Marlow Solar, LLC | Solar | 2 MW | 2020 |
Planned generation 2
| Plant | Technology | MW | Status | Year | Owner |
|---|---|---|---|---|---|
| Casey Fork Solar, LLC | Solar Photovoltaic | 150 MW | Built, not yet operating | 2026 | RWE Clean Energy |
| Harper Creek Solar, LLC | Solar Photovoltaic | 5 MW | Under construction (≤50%) | 2026 | Dimension Energy LLC |
The Jefferson County labor market
| Industry (2025) | Jobs | Average pay | Concentration vs U.S. |
|---|---|---|---|
| All industries | 19,432 | $59,848 | 1.00 |
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 Jefferson County
No data center, local measure or delayed project is on record in Jefferson County. Illinois has 28 local measures on record statewide.
Jefferson County and its neighbors
Of the 6 counties that border Jefferson County, Perry 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 |
|---|---|---|---|---|---|---|
| Jefferson County | 36,147 | ▼ 2.4% | 2 MW | 155 MW | — | — |
| Franklin County | 36,916 | ▲ 0.6% | 2 MW | — | — | — |
| Hamilton County | 7,859 | ▲ 3.0% | 6 MW | — | — | — |
| Marion County | 36,382 | ▼ 4.3% | 372 MW | — | — | — |
| Perry County | 20,160 | ▼ 5.2% | 535 MW | 168 MW | — | — |
| Washington County | 13,564 | ▼ 6.6% | 5 MW | — | — | — |
| Wayne County | 15,882 | ▲ 2.4% | — | — | — | — |
More of Illinois
Jefferson County, answered from the record
Who provides electricity in Jefferson County, Illinois?
3 utilities have service territory in Jefferson County in the EIA-861 2024 report: Ameren Illinois Company, Tri-County Electric Coop, Inc (IL), Wayne-White Counties Elec Coop. The largest, Ameren Illinois Company, charged residential customers 15.26¢/kWh on average in 2024.
What county is Mount Vernon, IL in?
Mount Vernon is in Jefferson County, Illinois. About 14,187 people live there (2025 Census estimate).
What county is Mount Vernon Township, IL in?
Mount Vernon Township is in Jefferson County, Illinois. About 12,192 people live there (2025 Census estimate).
What power plants are in Jefferson County?
1 operating plant with 2 MW of capacity. The largest is Marlow Solar, LLC CSG (2 MW, solar).
How much new power is planned in Jefferson 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 RWE Clean Energy.
Are there data centers in Jefferson County?
The SAVRN Data Center Map has no data center in Jefferson County.
Is Jefferson County adding jobs?
Employers counted 19,432 jobs in 2025 against 19,915 in 2019 (-2.4%, BLS QCEW).
Does Jefferson County have a data center moratorium?
No county-level measure is on record for Jefferson County. Illinois has 28 local measures statewide, listed on the state page.