This action relates to determinations of whether certain nonattainment areas for the 2015 ozone National Ambient Air Quality Standards (NAAQS) attained by the attainment date, based on the areas’ design values as of the attainment date. Specifically, the action finalizes determinations for 2015 ozone NAAQS nonattainment areas currently classified as Marginal. All Marginal areas must attain the ozone standard within 3 years of the effective date of the designation, or by August 3, 2021 (September 24, 2021 for the San Antonio, TX area), unless an area is granted a 1-year attainment date extension. If a Marginal area fails to attain the standard by the attainment date, the area will be reclassified to the higher of 1) the next higher classification for the area or 2) to the classification applicable to the area’s design value by operation law. In this notice, the U.S. Environmental Protection Agency finds that certain Marginal nonattainment areas attained the standard by the attainment date; one area requested and was granted a 1-year attainment date extension; and other areas failed to attain and will be reclassified.