Use of irrigated cornfields by small mammals was investigated in the sandsage prairie region of southwestern Kansas. Nine species were caught in cornfields during one year of sampling. Onychomys leucogaster, Peromyscus maniculatus, and Mus musculus were abundant residents, Perognathus flavescens, P. hispidus, and Reithrodontomys megalotis were resident but less abundant, and Dipodomys ordii was resident only during part of the year. Spermophilus spilosoma and Sigmodon hispidus were transients, whereas Peromyscus leucopus and Reithrodontomys montanus were available but not trapped in cornfields. Richness, evenness, and diversity are given for three habitats sampled (corn, edge areas, and grazed sandsage prairie). Data on relative densities, recruitment, movement, and reproduction are given for the species trapped.