The Environmental Protection Agency (EPA) is approving, under the Clean Air Act (CAA), revisions to the State Implementation Plan (SIP) submitted by the Illinois Environmental Protection Agency (Illinois EPA) on October 22, 2020, and February 14, 2023. The revisions address the emissions inventory requirements for the Chicago and Metro-East nonattainment areas under the 2015 ozone National Ambient Air Quality Standard (NAAQS or standard). The Chicago nonattainment area includes Cook, DuPage, Grundy (Aux Sable and Goose Lake Townships), Kane, Kendall (Oswego Township), Lake, McHenry, and Will counties. The Metro-East nonattainment area includes Madison, Monroe, and St. Clair counties. The CAA requires emissions inventories for all ozone nonattainment areas.