Sylvatic plague is one of the major impediments to the recovery of the black-footed ferret (Mustela nigripes) because it decimates their primary prey species, prairie dogs (Cynomys spp.), and directly causes mortality in ferrets. Fleas are the primary vector of Yersinia pestis, the causative agent of sylvatic plague. The goal of this research was to better understand the flea fauna of ferrets and the factors that might influence flea abundance on ferrets. Fleas from ferrets were tested for Y. pestis in a post hoc assessment to investigate the plausibility that some ferrets could act as incidental transporter hosts of fleas infected with Y. pestis. Fleas were collected from ferrets captured on the Lower Brule Indian Reservation in central South Dakota, US from 2009 to 2012. A total of 528 fleas collected from 67 individual ferrets were identified and tested for the presence of Y. pestis with a nested PCR assay. The predominant flea recovered from ferrets was Oropsylla hirsuta, a species that comprises 70–100% of the fleas recovered from prairie dogs and their burrows in the study area. Yersinia pestis was detected at low levels in fleas collected from ferrets with prevalence ranging from 0% to 2.9%; male ferrets harbored significantly more fleas than female ferrets. Six of 67 ferrets vaccinated against plague carried fleas that tested positive for Y. pestis, which suggests ferrets vaccinated against plague could inadvertently act as incidental transporter hosts of Y. pestis–positive fleas.