The world fauna of the genus HemicrepidiusGermar, 1839 is redefined and its species revised for North America. The genus is defined based on characteristics of female internal genitalia, with other characters used as support. Molecular analyses were also conducted to test the hypothesis that internal female genitalia can be used to diagnose genera in Elateridae and to test support for removing some species from synonymy. A key, diagnoses, illustrations, and synonymical tables to North American species are provided. Asaphites is removed from synonymy with Oxynopterinae and returned to synonymy with Hemicrepidiina. YukaraKishii, 1962 and MedakathousKishii, 1964 are returned to synonymy with Hemicrepidius. Two species are described: Hemicrepidius brooksi Etzler, new species (western North America) and Hemicrepidius mescalero Etzler, new species (New Mexico). Three species are removed from synonymy and recognized as valid: Hemicrepidius decoloratus (Say, 1836), status resurrected, Hemicrepidius melanopthalmus (Melsheimer, 1846), status resurrected, and Hemicrepidius ruficornis (Kirby, 1837), status resurrected. Lectotypes are designated for: Athous aereus Melsheimer, 1848, Athous cavifrons Melsheimer, 1848, Athous melanopthalmus Melsheimer, 1848, Diacanthus corporosusGermar, 1843, and Elater memnoniusHerbst, 1806. Neotypes are designated for Elater bilobatusSay, 1836 and Elater decoloratusSay, 1836. Five species and subspecies in Eurasia are returned to Hemicrepidius from other genera: Hemicrepidius amami Kishii, 1985, restored combination, Hemicrepidius dauricus (Mannerheim, 1852), restored combination, Hemicrepidius inornatus (Lewis, 1894), restored combination, Hemicrepidius jactatus babai (Ôhira, 1956), restored combination, and Hemicrepidius jactatus jactatus (Lewis, 1894), restored combination. Two species are transferred from MegathousReitter, 1905 to Hemicrepidius: Hemicrepidius jacobsoni (Reitter, 1905), new combination and Hemicrepidius nigerrimus (Desbrochers des Loges, 1869), new combination. Thirteen species of Hemicrepidius from Central America are transferred to Athous Eschscholtz, 1829, creating the following new combinations: Athous acuminatus (Champion, 1896), new combination, Athous bivittatus (Champion, 1896), new combination, Athous candezei (Champion, 1896), new combination, Athous consanguineus (Champion, 1896), new combination, Athous consobrinus (Champion, 1896), new combination, Athous cruciatus (Champion, 1896), new combination, Athous flavipes (Candèze, 1863), new combination, Athous germanus (Champion, 1896), new combination, Athous instabilis (Candèze, 1863), new combination, Athous nitidus (Champion, 1896), new combination, Athous parvulus (Champion, 1896), new combination, Athous patruelis (Champion, 1896), new combination, Athous pictipes (Chevrolat, 1843), new combination. One South American species is removed from Hemicrepidius and placed in PomachiliusCandèze, 1860, Pomachilius longipennis (Candèze, 1863), new combination. Asaphes longicollisCandèze, 1863 is reduced to synonymy with Athous deceptor (Candèze, 1863), new combination, status resurrected, the next available name for the species, to prevent secondary homonymy with Elater longicollis Olivier, 1790, previously recognized as valid within Athous. Two species require new names with the transfer of the species to Athous: Athous chicamensis Etzler, new replacement name for Hemicrepidius biformisChampion, 1896, to prevent secondary homonymy with Athous biformis Redtenbacher, 1859, and Athous chiriqui Etzler, new replacement name for Hemicrepidius longicornisChampion, 1896, to prevent secondary homonymy with Athous longicornisCandèze, 1865.