NRG Energy announced Thursday that it will cease coal operations at one of two generating units at its Romeoville plant and convert its Joliet plant to natural energy.
The move will eliminate 250 jobs.
Both power plants are coal-fired and have been under pressure for years by environmentalists and regulators to reduce emissions.
New Jersey-based NRG took over four plants in Illinois in April when it acquired Edison Mission Energy. The company also announced plans to install emissions control technology at plants in Waukegan and Pekin.
NRG said the moves announced Thursday will reduce overall carbon dioxide emissions by at least 16 million tons by 2020.