Onthophagus howdeni Zunino and Halffter was originally described from two male specimens collected in Oaxaca, Mexico. Thirty years later, this species is collected again in the Sierra Norte of Oaxaca, the previously unknown female is described, and information about its biology is given. Onthophagus zapotecus Zunino and Halffter was originally described based on three specimens. A redescription of this species is based on newly collected specimens. New data are provided on the distribution of Onthophagus howdenorum Zunino and Halffter, Onthophagus oaxacanus Zunino and Halffter, Onthophagus aureofuscus Bates, and O. zapotecus. The International Union of Conservation of Nature's status of O. aureofuscus and Onthophagus undulans Bates are examined. The affinities with other species of the species- group are discussed, and information about their biology and capture method is presented. An identification key is given, in English and Spanish, for the species of Onthophagus Latreille recorded in Sierra Norte and Sierra Sur of Oaxaca.