The Environmental Protection Agency (EPA) is approving revisions to the Illinois State Implementation Plan (SIP) that were submitted by the Illinois Environmental Protection Agency (IEPA) on September 22, 2020, and amended on November 5, 2020, and March 3, 2021. These revisions implement new preconstruction permitting regulations for certain new or modified sources of air pollution in attainment and unclassifiable areas under the Prevention of Significant Deterioration (PSD) program of the Clean Air Act (CAA). EPA is also transferring to IEPA responsibility for administering existing PSD permits that EPA previously issued to sources in Illinois, and for processing any PSD permit actions related to such permits.