A list of diatom taxa from inland waters of the northwestern United States is presented as a product of the author's bioassessment work over the last 40 years. The list is limited to taxa that have been identified from slides that are deposited in the Montana Diatom Collection. The list includes 1,348 species and infra-species taxa in 118 genera. The list is provided in support of recent efforts to compile a comprehensive and up-to-date diatom flora for the conterminous United States. Slides, acid-cleaned material, geospatial data, and/or ecological data for taxa in the checklist are available from the author.