The othonus species-group of Nearctic Pachybrachis Chevrolat, 1836 is defined and revised. The group is composed of five species, including one described as a new species: Pachybrachis nigricornis (Say), Pachybrachis othonus (Say), Pachybrachis pallidipennis Suffrian, Pachybrachis praeclarus Weise, and Pachybrachis armbrusti Barney, new species. Subspecies designations for P. nigricornis and P. othonus are eliminated. Pachybrachis othonus sioux Balsbaugh and Pachybrachys litigiosus Suffrian are synonymized with P. othonus (Say) (new synonymy), and P. othonus pallidipennis Suffrian is elevated to species rank (new status). Pachybrachis nigricornis autolycus Fall, Pachybrachis nigricornis carbonarius Haldeman, Pachybrachis nigricornis difficilis Fall, Pachybrachis nigricornis nigricornis (Say), Pachybrachis autolycus janus Fall, and Pachybrachis autolycus wahsatchensis Fall are all synonymized with P. nigricornis (Say) (new synonymies). A key to species is given, and a description, figure, and range map is presented for each species.