The American species of Cosmetidae, in spite of being clearly distinguished in the older literature, were mixed-up by Roewer. This, aggravated by groundless synonymies done by Goodnight & Goodnight, prevented all subsequent authors from properly recognizing and adequately naming those species. Herein, we define and characterize the three most widespread species of Cosmetidae in the USA, explaining the misleading synonymies and misidentifications in the taxonomic literature. A recent phylogenetic analysis revalidated Libitioides Roewer, 1912 from the synonymy of Vonones Simon, 1879 to include three American species: Gonyleptes ornatum Say, 1821 (from southeastern USA), Cynorta sayi Simon, 1879 (from central-southern USA) and Cosmetus albolineatus Sørensen, 1884 (from eastern USA). Expanding on that, we herein aggregate another two species to Libitioides: Vonones modestus Banks, 1909 (from Cuba, herein revalidated from the synonymy of Libitioides ornata Roewer, 1912) and Libitioides scabrissima Roewer, 1912 (from Mexico, restored from the current combination with Vonones). The following subjective synonymies are proposed: (1) Platycynorta Mello-Leitão, 1933 and Denticynorta Roewer, 1947 = Libitioides; (2) Metacynorta denticus Walker, 1928 = Cosmetus albolineatus; (3) Platycynorta secunda Roewer, 1947 = Vonones modestus; (4) Libitioides ornata Roewer, 1912 and Cynorta (Cynorta) depressa Sørensen, 1932 = Cynorta sayi. Outside Libitioides, Cynorta bimaculata Banks, 1893, currently combined under Calicynorta Goodnight & Goodnight, 1943, and originally reported from California (due to a misinterpretation of label) has its type locality corrected as to be in Costa Rica instead and is transferred to Holovonones Roewer, 1912. Accordingly, Calicynorta is herein considered a junior subjective synonym of Holovonones Roewer, 1912. Platycynorta clavifemur Roewer, 1957 from Peru is newly combined under the genus Ambatoiella Mello-Leitão, 1943, otherwise known from Ecuador. The present analysis of the distributional data suggests that the occurrence of Cosmetidae is determined not directly by temperature, but by the absence of a dry season and the presence of a hot summer.