We investigate the species-level taxonomy and evolutionary history of Nearctic ants in the Crematogaster scutellaris group (Hymenoptera: Formicidae), drawing on evidence from morphology and UCE (ultraconserved element) phylogenomics. The New World species in this group form a well supported clade that originated in the late Miocene (~7.3 Ma) and subsequently diverged into three major lineages: the coarctata clade (southwest Nearctic), the opaca clade (southwest Nearctic and northern Neotropics), and the lineolata clade (eastern Nearctic and Caribbean, with four isolated Southwest endemics). We hypothesize trans-Beringian dispersal into the New World, west-to-east movement within North America, and restriction of mesophilic species to the east with increasing aridification of the west. The ancestral nesting behavior of these ants is inferred to be ground-dwelling, and this is still the predominant condition in the arid west, whereas most species in eastern United States are arboreal. We resurrect from synonymy nine species, and describe three new species: C. detecta sp. nov. (from Nevada), C. parapilosa sp. nov. (Florida), and C. vetusta sp. nov. (Arizona). We provide a worker-based key to the thirty-four species of Crematogaster occurring in America north of Mexico, but emphasize that there are still ongoing taxonomic issues that need to be resolved.