The atomarius species-group of Nearctic PachybrachisChevrolat, 1836 is defined and revised. The group is composed of 24 species: Pachybrachis archboldi Barney; Pachybrachis atomarius (F. E. Melsheimer); Pachybrachis calcaratus Fall; Pachybrachis caroleae Barney, new species; Pachybrachis cephalicus Fall; Pachybrachis charlotteae Barney, new species; Pachybrachis confederatus Fall; Pachybrachis conformis Suffrian; Pachybrachis dixianus Fall; Pachybrachis erinae Barney, new species; Pachybrachis gibbyi Barney, new species; Pachybrachis gibsoni Barney, new species; Pachybrachis jacobi Barney, new species; Pachybrachis lodingi Bowditch; Pachybrachis luctuosus Suffrian; Pachybrachis matthewi Barney, new species; Pachybrachis mcmeansi Barney, new species; Pachybrachis osceola Fall; Pachybrachis parvus Fall; Pachybrachis quadrioculatus Fall; Pachybrachis relictus Fall; Pachybrachys stygicus Fall; Pachybrachis varians Bowditch; and Pachybrachis walteri Barney, new species. Pachybrachis cephalicus var. dixianus Fall and P. cephalicus var. parvus Fall are elevated to full species status (new status). Pachybrachis carolinensis Fall is synonymized under P. luctuosus (new synonymy), Pachybrachis vestigialis Fall is synonymized under P. stygicus (new synonymy), and Pachybrachis tybeensis Fall is synonymized under P. confederatus (new synonymy). Forty-eight new state records are confirmed for previously named members of this species-group. A key to species is given, and a description, figure, and range map are presented for each species.