The predatory beetle assemblage of Ontario carrot and sweet potato fields was described and assessed to identify species of interest to the control of the emerging pest millipede Cylindroiulus caeruleocinctus (Wood) (Diplopoda: Julidae). Pterostichus melanarius (Coleoptera: Carabidae) was identified as a dominant species, and seven other carabid species [Pterostichus melanarius (Illiger), Harpalus pensylvanicus (DeGeer), Ophonus puncticeps (Stephens), H. erraticus Say, Bembidion quadrimaculatum oppositum Say, Poecilus chalcites (Say), Scarites subterraneus Fabricius, and Pterostichus permundus (Say)] were identified as common species on the basis of activity density. Common species became more abundant as the growing season progressed. In laboratory bioassays, P. melanarius preyed on millipedes regardless of prey size, whereas H. erraticus never selected millipedes as prey. A significant positive spatiotemporal relationship was found between P. melanarius and C. caeruleocinctus in sweet potato fields. P. melanarius was found to be a natural enemy of C. caeruleocinctus, and other common carabid species warrant future study. The role of Staphylinidae in millipede control could not be elucidated, likely because of low trapping efficiency. Tachinus corticinus Gravenhorst, an introduced staphylinid from Europe, was newly recorded in Ontario, extending its North American range considerably westward from the province of Quebec. The results of this study are an important foundational step toward developing a successful integrated pest management strategy for controlling millipede damage in crops.