Seven characters were evaluated in 146 specimens of Gomphus fraternus (Say), including both subspecies, G. f. fraternus (Say) and G. f. manitobanus Walker, to clarify their circumscription and geographic occurrence in Canada. Specimens corresponding to subspecies manitobanus were all from the Assiniboine and Red rivers and formed a discrete group in a principal components analysis, supporting their taxonomic recognition. Their distribution in Canada suggests a separation of subspecies near the boundary of the prairie ecozone in central southern Manitoba. In subspecies fraternus the extensor surfaces of the tibiae are largely black, with pale areas often lacking and rarely up to 50% of the segment length. Similarly the dorsal surface of abdominal segment 9 is largely black. If there is a pale area, it is <1 mm long. In subspecies manitobanus the extensor surfaces of the tibiae have pale markings on ≥50% of their lengths and the dorsal surface of abdominal segment 9 has a dorsal yellow spot ≥1.4 mm long. Widespread dragonflies in western North America are paler in drier climates and the increased pale colouration in the western subspecies manitobanus corresponds to this trend. Currently known only from Manitoba, subspecies manitobanus may occur in prairie habitats of the Midwestern United States, based on reports of pale individuals in that region.