The Environmental Protection Agency (EPA) is approving two Mississippi State Implementation Plan (SIP) revisions from the Mississippi Department of Environmental Quality (MDEQ) dated October 4, 2018, and August 13, 2020. The October 4, 2018, SIP revision contains the State's first periodic report describing progress towards reasonable progress goals (RPGs) established for regional haze and contains the associated determination that the State's regional haze SIP is adequate to meet these RPGs for the first implementation period (Progress Report). The August 13, 2020, SIP revision addresses best available retrofit technology (BART) determinations for 14 electric generating units (EGUs) (BART SIP). These EGUs were initially addressed in EPA's prior limited approval and limited disapproval actions on Mississippi's regional haze SIP because of deficiencies arising from the State's reliance on the Clean Air Interstate Rule (CAIR) to satisfy certain regional haze requirements. EPA is approving the BART SIP and finds that it corrects the deficiencies that led to the limited approval and limited disapproval of the State's regional haze SIP. EPA is therefore withdrawing the limited disapproval of Mississippi's regional haze SIP and replacing the prior limited approval with a full approval of the regional haze SIP as meeting all regional haze requirements of the Clean Air Act (CAA or Act) for the first implementation period. EPA is also approving the Progress Report and associated adequacy determination.