Observing mating behaviors in wild populations is difficult because of the relative infrequency of copulations, nocturnal habits of many species, and possible observer effects on behavior. However, the development of genetic techniques has enabled the outcome of reproductive activities to be examined by sampling young and potential parents. Our objective was to examine paternity in a population of free-ranging raccoons (Procyon lotor) in southern Illinois using 10 highly polymorphic microsatellite markers. We determined genotypes for 183 individuals, including 35 young from 11 litters. Most litters (X̄ = 3.2 young/litter ± 0.4 SE) had multiple sires, as indicated by >2 paternal alleles at each locus; ≥88% of 8 litters with >2 young were sired by multiple males. These results indicate that females mate with multiple males during estrus. We also found evidence that at least 1 male mated with multiple females. Sires (75%; n = 8) were usually trapped <500 m from the locations where dams were trapped. In this raccoon population, the mating system is best described as promiscuous. We hypothesize that this pattern of breeding behavior is influenced by a male-biased sex ratio and high population density of raccoons on the study area.