The purpose of this data release and associated data series (Carr and Fancher, in review) was to compile occurrence records and map the distribution of a freshwater mussel assemblage for the Bureau of Land Management Rapid Ecoregional Assessment for the Southern Great Plains. The freshwater mussel assemblage includes Amblema plicata (threeridge), Fusconaia flava (Wabash pigtoe), Lampsilis cardium (plain pocketbook), Lampsilis teres (yellow sandshell), Pyganodon grandis (giant floater), and Uniomerus tetralasmus (pondhorn). The focal species in the assemblage were selected based on the following criteria: (1) the species are regionally significant, (2) occurrence records are sufficient to map the distribution of the species by hydrological subbasins, (3) the status of each species includes a range of State-level conservation priorities, and (4) the species are not listed as federally endangered or threatened. The six focal species represent a broad array of life history traits and habitat associations. The contemporary distribution (survey dates: 1970 to 2017) were mapped at two spatial scales: hydrological subbasins and subregions within the Missouri and Arkansas-White-Red Regions. Historical records (occurrence record dates: 1885 to 1962) were also compiled but were limited. This data release summarizes occurrence records for the freshwater mussel assemblage by the 8-digit hydrologic unit code, which identifies the region, subregion, and subbasin. For each subbasin, the data release provides occurrence information for each of the six focal species, including the data source, time period, and number of records. Such multiscale baseline information can be useful for evaluating mussel population status and trends, identifying potential restoration areas, and providing the broader context for in-depth studies within watersheds, reaches, and subcatchments. Additional background information, methods, dataset limitations, and graphical representations of this data release, are provided in the associated data series available at https://doi.org/ 10.3133/ ds1133.