This technical note provides an illustrated key to the 13 genera and a checklist for the 178 currently recognized species of freshwater, inland saline, and estuarine truncatelloidean gastropods (primarily belonging to the families Amnicolidae, Cochliopidae, Hydrobiidae, Lithoglyphidae, and Tateidae) in the western United States. It also outlines methods of specimen preparation and dissection to facilitate use of the generic key. The checklist includes bibliographic information for each species (and their synonyms), type localities, type material, and geographic distributions. The appendix includes a comprehensive synopsis of the available DNA barcoding sequences (the COI gene, cytochrome c oxidase subunit I) for members of this fauna in the anticipation that these data will be increasingly used for both taxonomic and conservation genetic applications. This technical note serves as an entry portal for resource managers, taxonomists, and other individuals interested in this species-rich and highly imperiled fauna.