Eight species of the siphonine genus Actia Robineau-Desvoidy are recognized in the Nearctic Region, including four that are new: A. dasymyia sp.nov. (type-locality 21 mi. east Tuktoyaktuk, North West Territories, Canada), A. dimorpha sp.nov. (type-locality Sapelo Island, Georgia, USA), A. radialis sp.nov. (type-locality Gatineau Park, Quebec, Canada), and A. sternalis sp.nov. (type-locality mi. 51 Dempster Highway, Yukon, Canada). Adults of the eight species are keyed, described, illustrated (heads, wings, and male terminalia), and their distributions mapped. The species are arranged into three species groups: the autumnalis-group with Nearctic members A. autumnalis (Townsend), A. rufescens (Greene), A. diffidens Curran, and A. dimorpha sp.nov.; the lamia-group with Nearctic members A. interrupta Curran, A. dasymyia sp.nov., and A. radialis sp.nov.; and the crassicornis-group with the single Nearctic member A. sternalis sp.nov. Nearctic Actia are inferred to be of relatively recent origin because only the A. autumnalis/A. rufescens species pair seems to have speciated within the Nearctic Region. Actia autumnalis/A. rufescens, A. diffidens, and A. dimorpha are each hypothesized to have their closest phylogenetic affinities with Neotropical species, and A. sternalis, A. interrupta, A. dasymyia, and questionably A. radialis are each hypothesized to have their closest affinities with Palearctic species.