Five species of Trichomalopsis Crawford associated with Haematobia irritans (L.) (horn fly), Musca domestica L. (house fly), Musca autumnalis DeGeer (face fly), and Stomoxys calcitrans (L.) (stable fly) in North America are reviewed. The species Trichomalopsis americana (Gahan), Trichomalopsis dubia (Ashmead), Trichomalopsis sarcophagae (Gahan), Trichomalopsis tachinae (Gahan), and Trichomalopsis viridescens (Walsh) are described, keyed, and differentiated from other recognized North American species. Lectotypes are designated for T. dubia, T. sarcophagae, and T. tachinae. Distribution and host associations are recorded for the species. Trichomalopsis americana and T. viridescens are newly recorded as parasitoids of M. domestica; T. dubia and T. sarcophagae are also newly recorded as parasitoids of Hypoderma lineatum (Villers) (common cattle grub) and Hypoderma bovis (L.) (northern cattle grub), respectively. Some previously published host associations and parasitoid identifications are corrected based on examination of voucher specimens. The known biology of each species is reviewed. The presence of Trichomalopsis albipilosa (Gahan) in North America is considered to be erroneous based on a misidentification of T. americana.