This final action revises or affirms the initial air quality designations for 14 counties associated with seven nonattainment areas for the 2015 primary and secondary National Ambient Air Quality Standards (NAAQS) for ozone. In a July 10, 2020, decision, the District of Columbia Circuit Court remanded to the Environmental Protection Agency (EPA or Agency), but did not vacate, the April 30, 2018, designations for 16 counties associated with nine nonattainment areas located in seven states. In response, the EPA has re-evaluated the designations for the remanded counties by applying a uniform, nationwide analytical approach and interpretation of the designation provisions of the Clean Air Act (CAA) in considering the specific facts and circumstances of the areas using only data and information available at the time of the original designations. In this final action, the EPA is revising the designations and/or boundaries of 13 counties associated with six nonattainment areas in four states (Illinois, Indiana, Missouri, and Wisconsin) and is affirming the April 30, 2018, designation of one county associated with a nonattainment area in Michigan. The EPA is addressing the two additional remanded counties associated with two nonattainment areas in a separate Federal Register document.