Dermacentor variabilis Say is a tick species widely distributed in North America, where it is a common pest, and acts as vector for many tick-borne pathogens that affect both humans and livestock. In the United States, D. variabilis has a discontinuous geographic distribution. It is present eastwards of a line drawn from Montana to southernTexas, and a few disjoint populations western of the Rockies and in the intermountain region. It has been hypothesized that both groups may correspond to different species.The aim of this study was to investigate the population genetic structure of, and potential speciation within, D. variabilis.To do this, we generated a new data set based on nuclear markers (SNPs) discovered through next-generation sequencing.The results showed moderate population structure and supported the occurrence of gene flow between some genetic clusters. Maximum parsimony phylogenetic reconstruction showed a divergent monophyletic western clade and a generally eastern clade. Overall, the nuclear data set analyzed herein is congruent with previous findings based on mitochondrial markers, although it led to a higher level of resolution within the eastern clade. Additional lines of evidence are needed to determine whether eastern and western populations correspond to different species.