Understanding population genetic structure provides insight into the evolutionary past, present, and future of a species. In this study, we examine the range-wide population genetic structure of the prairie vole, Microtus ochrogaster (n = 170). Early work divided M. ochrogaster into seven subspecies using morphological characteristics. We hypothesized polymorphic microsatellite data would reveal a genetic structure roughly congruent with the current classification of subspecies based on their geographic boundaries. We predicted populations within the geographic range of one subspecies would be genetically distinguishable from populations within the geographic range of another subspecies. Microsatellite data from the seven putative subspecies suggested ∼90% of molecular variation was within populations. A STRUCTURE cluster analysis had a best supported k = 3, but most individuals were admixed for the three genetic clusters, and only individuals of M. o. ohionensis were distinctive in being essentially represented by a single cluster. Therefore, our molecular data showed evidence of relatively high gene flow and little geographic differentiation throughout the range of the six contiguous subspecies. The subspecific classification of M. ochrogaster should be re-evaluated using a comprehensive taxonomic approach that combines molecular, morphometric, and other data.