The purpose of this study was to determine the species of fleas infesting the mammals of the families Cricetidae and Muridae in Utah County. This was accomplished by establishing twelve collecting stations throughout the county from which 198 mammals were collected. From these hosts, 392 fleas were collected representing three families, nineteen genera , and twenty-four species. Four species are new to the State of Utah and twenty-two species are recorded from Utah County for the first time.