New state, Upper Peninsula, and county records of mayflies from the Upper Peninsula of Michigan, U.S.A., are provided. Included are the first Michigan records of eleven species of mayflies, including five from the Family Baetidae [Acentrella nadineae McCafferty, Waltz, and Webb, Anafroptilum minor (McDunnough), Labiobaetis frondalis (McDunnough), Plauditus cestus (Provonsha and McCafferty), and Procloeon rivulare (Traver)], two from Caenidae [Caenis hilaris (Say), and Caenis tardata McDunnough], two from Heptageniidae [Maccaffertium mexicanum integrum (McDunnough), Nixe inconspicua (McDunnough)], one from Isonychiidae [Isonychia sicca (Walsh)], and one from Leptohyphidae [Tricorythodes robacki (Allen)]. In addition, the first Upper Peninsula records are given for eight mayfly species with previously published records from elsewhere in Michigan.