In Williamson County, Illinois (IL). The map on this page is placed at the coordinates EIA files for the plant, which locate the site rather than any individual unit.

249 MW of nameplate capacity across 5 units, as of the EIA-860M release for 2026-07.

EIA-860M names Southern Illinois Power Coop as the reporting entity. That is the operator of record on the survey, which is not always the ultimate owner.

Is this the same as Marion LLC?

Probably, but EIA-860M does not say. The survey records a plant name and a reporting entity — Southern Illinois Power Coop here — not the project company that holds the asset. Project companies are commonly registered as an LLC carrying the plant's name, so a search for "Marion LLC" usually means this site. This page shows only what EIA files, and does not assert a corporate structure it cannot see.

Is Marion still running?

EIA-860M files it as "Operating" for 2026-07. Statuses change monthly, and this page follows the monthly release.

Marion

Marion is a 249 MW natural gas power plant in Williamson County, Illinois, operated by Southern Illinois Power Coop. EIA-860M lists 5 generating units here, inside MISO. Its units entered service between 1963 and 2003.

As of 2026-07 (inventory dated 2026-07-31) · EIA-860M Preliminary Monthly Electric Generator Inventory · eia.gov/…/july_generator2026.xlsx · eia.gov/…/eia860m

Nameplate capacity: 249 MW; 260 MW net summer
Generating units: 5
In service: 1963–2003
EIA plant ID: 976

Where it is

Loading map…

County: Williamson County, Illinois
Coordinates: 37.6197, -88.9531
Balancing authority: MISO
Sector: Electric Utility

Units, technology and status

Operator of record: Southern Illinois Power Coop
Primary energy source: Natural gas
Technologies: Conventional Steam Coal, Natural Gas Fired Combustion Turbine
Status: Operating

This site runs on more than one energy source. EIA-860M capacity splits: Natural gas 150 MW, Coal 99 MW. It is filed here under Natural gas, the source with the most capacity.

Every plant Southern Illinois Power Coop reports to EIA →

Marion: FAQ

Where is Marion?: In Williamson County, Illinois (IL). The map on this page is placed at the coordinates EIA files for the plant, which locate the site rather than any individual unit.
How big is Marion?: 249 MW of nameplate capacity across 5 units, as of the EIA-860M release for 2026-07.
Who owns Marion?: EIA-860M names Southern Illinois Power Coop as the reporting entity. That is the operator of record on the survey, which is not always the ultimate owner.
Is this the same as Marion LLC?: Probably, but EIA-860M does not say. The survey records a plant name and a reporting entity — Southern Illinois Power Coop here — not the project company that holds the asset. Project companies are commonly registered as an LLC carrying the plant's name, so a search for "Marion LLC" usually means this site. This page shows only what EIA files, and does not assert a corporate structure it cannot see.
Is Marion still running?: EIA-860M files it as "Operating" for 2026-07. Statuses change monthly, and this page follows the monthly release.