Marion

Natural gas power plant · Williamson County, Illinois

Nameplate capacity
249 MW
Rank in Illinois
#50
of 580 plants
In service since
1963
June 1963

Details

Primary fuel
Natural gas
Technology
Natural Gas Fired Combustion Turbine
Operator
Southern Illinois Power Coop
County
Williamson County
Generating units
5
Share of state capacity
0.47%
Rank among natural gas plants in Illinois
#28 of 72
EIA plant code
976

Generating units

Individual generating units at Marion
UnitTechnologyNameplateSummerOnlineStatus
5Natural Gas Fired Combustion Turbine75 MW70 MW2003Operating
6Natural Gas Fired Combustion Turbine75 MW70 MW2003Operating
1Conventional Steam Coal33 MW40 MW1963Operating
2Conventional Steam Coal33 MW40 MW1963Operating
3Conventional Steam Coal33 MW40 MW1963Operating

Nameplate is the maximum rated output; summer capacity is what the unit can reliably deliver on a hot day, which is typically lower.

Similarly sized plants in Illinois

About this data

From EIA’s inventory of operable generators, May 2026 release. Capacity is nameplate — the maximum rated output of the equipment, not what the plant actually generates over a year, which depends on how often it runs. A 249 MW solar plant and a 249 MW nuclear plant have the same entry here and produce very different amounts of electricity.

“In service since” is the earliest in-service date among the units still listed, so a site rebuilt around newer equipment can read as younger than the site itself. All Illinois power plants · What Illinois actually generates