Piñon-juniper woodland is expanding across much of western North America. In the Great Basin, woodland expansion has encroached on native shrublands, threatening species that have close associations with the sagebrush ecosystem. Piñon-juniper woodlands also harbor great biodiversity, and the response of woodland specialists to expansion has been less well studied than that of shrubland specialists. Here, we use occupancy and abundance modeling, accounting for imperfect detection, to assess habitat use of a woodland specialist, the piñon mouse (Peromyscus truei). Our study occurred in the Toiyabe Range of central Nevada, an area P. truei is thought to have recently colonized. Understanding habitat use at an expanding range margin can have important implications for dispersal-mediated woodland expansion. Peromyscus truei was documented in a wide range of conditions, including nonwoodland and woodland habitats, across the latitudinal and elevational extent of the mountain range. Occupancy models suggest that P. truei occurrences are most associated with the presence of piñon pine. For abundance, our global model was the best supported, indicating that no one environmental factor or set of factors considered were found to structure abundance. Chi-square tests indicate that use of woodland versus nonwoodland habitats by P. truei is not structured by age or sex. Although P. truei was found in a range of habitat types, we cannot conclude whether it is more appropriate to characterize this species as a habitat generalist, or whether postcolonization abiotic and biotic filtering is not yet complete. Research on woodland specialists at expanding local and landscape-scale range margins provides a unique opportunity to study how habitat selection and ecological filtering impact community assembly under environmental change.