This study documents a comprehensive taxonomic treatment of the New World Ummidia species. At the onset of this work the genus comprised 27 species and one subspecies with a cosmopolitan distribution that includes North America, South America, Asia, northern Africa, and Europe; of these species the majority of the nominal diversity can be attributed to the New World where 20 species have been previously described. Ummidia oaxacana (Chamberlin, 1925) is considered a nomen dubium; U. tuobita (Chamberlin, 1917) and U. absoluta (Gertsch and Mulaik, 1940) are both considered junior synonyms of U. audouini (Lucas, 1835); the subspecies U. carabivora emarginata (Atkinson, 1886) is considered a junior synonym of U. carabivora (Atkinson, 1886); U. pygmaea (Chamberlin and Ivie, 1945) is considered a junior synonym of U. beatula (Gertsch and Mulaik, 1940); U. celsa (Gertsch and Mulaik, 1940) is considered a junior synonym of U. funerea (Gertsch, 1936); Hebestatis lanthanus (Valerio, 1987) is considered a junior synonym of U. rugosa (Karsch, 1880). Thirty-three new species are described: U. neilgaimani, U. gingoteague, U. rongodwini, U. okefenokee, U. richmond, U. macarthuri, U. colemanae, U. rosillos, U. mercedesburnsae, U. paulacushingae, U. waunekaae, U. gertschi, U. timcotai, U. gabrieli, U. pesiou, U. rodeo, U. huascazaloya, U. anaya, U. cuicatec, U. brandicarlileae, U. riverai, U. frankellerae, U. hondurena, U. yojoa, U. matagalpa, U. carlosviquezi, U. varablanca, U. quepoa, U. cerrohoya, U. quijichacaca, U. tibacuy, U. neblina, U. tunapuna.