Twenty-three Ephemeroptera species are reported variously from four Central American countries (Costa Rica, Honduras, Nicaragua, Panama) and nine Mexican states (Chiapas, Durango, Guanajuato, Guerrero, Hidalgo, Oaxaca, Puebla, Queretaro, San Luis Potosi) for the first time. Campsurus decoloratus, Fallceon nikitai, and Tricorythodes explicatus are reported from Central America for the first time. Allenhyphes vescus is reported from southern Mexico for the first time, and second ever records are given for Choroterpes ungulus (Durango), and Leptohyphes priapus (Panama). Published record based checklists for the 28 Mexican states with reported mayflies are provided. The greatest diversity is found in Vera Cruz followed in order by Chihuahua, Chiapas, Tamaulipas, Neuvo Leon and Queretaro. Baetis magnus, Callibaetis pictus, Camelobaeitidus mexicanum, Fallceon quilleri, Neochoroterpes Oklahoma, Thraulodes brunneus, Traverella albertana and Vacupernius packeri are among the most commonly encountered mayflies in Mexico.