Conservation of wide-ranging species is aided by population genetic information that provides insights into adaptive potential, population size, interpopulation connectivity, and even extinction risk in portions of a species range. The Striped Whipsnake (Masticophis taeniatus) occurs across 11 western U.S. states and into Mexico but has experienced population declines in parts of its range, particularly in the state of Washington. We analyzed nuclear and mitochondrial DNA extracted from 192 shed skins, 63 muscle tissue samples, and one mouth swab to assess local genetic diversity and differentiation within and between the last known whipsnake populations in Washington. We then placed that information in a regional context to better understand levels of differentiation and diversity among whipsnake populations in the northwestern portion of the range of the species. Microsatellite data analyses indicated that there was comparable genetic diversity between the two extant Washington populations, but gene flow may be somewhat limited. We found moderate to high levels of genetic differentiation among states across all markers, including five microsatellites, two nuclear genes, and two mitochondrial genes. Pairwise state-level comparisons and dendrograms suggested that Washington whipsnakes are most closely related to those in Oregon, and distinct from Idaho, Nevada, and Utah, approximately following an isolation by distance model. We conclude that Washington populations of whipsnakes have experienced recent isolating events, but they have yet to lose genetic diversity. The longevity and high vagility of the species may provide opportunity for conservation of whipsnakes in the state as long as shrubland habitat is available