San Joaquin kit foxes (Vulpes macrotis mutica) are typically socially monogamous. During the 2012 breeding season in Bakersfield, California, where food is abundant, population density is high, and dispersal potential is low, we documented two cases of social polygyny. Both groups had two litters; we documented allonursing in one group. In both groups the two mothers were not closely related and the “helper” was not closely related to the other adults. All four reproducing females had at least one pup sired by an extragroup male. One female had three inbred pups that resulted from matings with first-degree relatives. The unique conditions associated with the urban environment may alter kit fox social ecology.