Age, sex, breeding, cost, source, and reproductive data on dog and cat populations were obtained for Champaign County, Illinois. Of 623 households from which completed interviews were obtained, 37.4% had 1 or more dogs, and 17.8% had 1 or more cats. The estimated population of dogs was 22,118 and of cats, 16,055, with a proportion to human population of 1 dog/7.4 persons and 1 cat/9.9 persons. The mean age of cats (2.98 yr) was about two-thirds of the mean age of dogs (4.64 yr); the median age of cats (1.8 yr) was about one-half the median age of dogs (3.7 yr). The most often mentioned origin of dogs was private pet owners; cats were most often reported as being offspring of currently owned cats. The proportion of households owning dogs and cats was higher in rural than in urban areas.