Twenty-three species and one variety belonging to three subgenera of the family Simuliidae are recorded and described. Of these, twelve species and the variety are new to science. Only two of the remaining eleven species of other authors have been previously recorded in Eastern Canada; two others, originally described in Europe, are recorded in North America for the first time, and the hitherto unknown male of a fifth species is described. The adult forms and the pupae and cocoons of these species are described, and the genitalia of both sexes of flies are figured. In addition, notes on the habitats, distribution, species associations, and similar information of value in identifying the species are given. Keys to the subgenera and species, including both sexes of adults and the pupae are an important feature.