A lack of quantitative information on life history of the western gray squirrel (Sciurus griseus) has hampered conservation and management efforts across its range. We report on data from 21 squirrels radiotracked in Klickitat County, Washington, from 1998 to 1999 to examine the interaction between home-range size, sex, and season. Home-range estimates were calculated by using minimum convex polygon and fixed kernel methods. Only adult animals with ≥40 relocations were included in total home-range comparisons. Estimates of 95% minimum convex polygon home range in Washington averaged 73.0 ha for males (n = 9) and 21.6 ha for females (n = 12) for year-round use, significantly larger than those from Oregon and California. Differences in home-range size of males and females were significant. Fixed kernel and minimum convex polygon estimates were similar in size. We suggest that near the northern limit of the species' geographic range low species richness, low abundance, and a patchy distribution of mast-producing vegetation result in large male and female home ranges, low overlap of female home ranges, and a sparsely distributed squirrel population.