Surveillance of mule deer (Odocoileus hemionus, Rafinesque, 1917) populations for tick-borne diseases has helped define the distribution of these pathogens and their subsequent risk of transmission to humans and domestic animals. We surveyed three mule deer herds across the state of Nevada for infection with relapsing fever Borrelia spp. spirochetes. Bacterial prevalence varied by the county where deer were sampled but Borrelia spirochetes were detected in 7.7% of all deer sampled. Infected deer were identified in every location from which mule deer samples were obtained. Sequencing of the Borrelia intergenic spacer gene (IGS) revealed that one individual was infected with Borrelia coriaceae and all others were infected with Borrelia hermsii. The vector of B. hermsii, Ornithodoros hermsi (Acari: Argasidae, Wheeler, Herms, and Meyer, 1935), feeds primarily on wild rodents and has not been identified infesting deer. Additionally, Ornithodoros coriaceus (Acari: Argasidae, Koch, 1844), which readily feeds on deer and is frequently infected with B. coriaceae, has not been shown to be a competent vector for B. hermsii. Our data represent the first sylvatic evidence of B. hermsii infection in mule deer. Additionally, our data provide evidence that infection with relapsing fever spirochetes in Nevada is wide ranging in the state's deer populations.