Numerous studies of forest fragmentation have found a negative relationship between density of Peromyscus leucopus and forest fragment size. This relationship may be caused by both more food, and more cover from predation in smaller fragments, which have more structurally complex understory vegetation than larger fragments. However, we do not know the extent to which the proximity of understory vegetation affects selection of nesting sites within fragments. We hypothesized that nest boxes in highly vegetated areas would be utilized more often by P. leucopus than nest boxes in sparsely vegetated areas. We tested this hypothesis by measuring the amount of vegetation near thirty nest boxes in each of nine forest fragments. We also estimated the relative population density of P. leucopus in each fragment. We expected to find both a greater proportion of nest boxes occupied and a greater number of mice in nest boxes with a high amount of nearby vegetation. In our nine study sites in southwest Ohio, the structural complexity of understory vegetation was significantly greater in small forest fragments than in large and in edge habitat than interior. However, there was no relationship between any of the variables we measured, such as soil moisture and tree diameter, in the immediate vicinity of nest boxes and the density of mice. In edge habitat and larger fragments, the population density of mice was greater and nest boxes were more frequently occupied. Our results suggest that the complexity of vegetation immediately surrounding the nest box may not be as important to mice as vegetation at a larger scale (throughout an individual’s territory).