Nine new species of Slaterocoris Wagner are described from North America: pilosus from British Columbia; alpinus from Colorado; apache from Arizona, Colorado, and Utah; flavipes, solidaginis, and sparsus from California; argenteus, grandis, and simplex from Durango, Mexico. The other species in the genus are: ambrosiae (Kngt.), atratus (Uhl.), atritibialis (Kngt.), breviatus (Kngt.), croceipes (Uhl.), hirtus (Kngt.), longipennis Kngt., mohri (Kngt.), pallidicornis (Kngt.), pallipes (Kngt.). robustus (Uhl.), rubrofemoratus Kngt., sheridani Kngt., stygicus (Say), and utahensis Kngt. Strongylocoris uniformis Van D. is placed in synonymy with Stiphrosoma robusta Uhl. Strongylocoris albibasis Knight does not belong to Slaterocoris and will be dealt with in a subsequent paper. All species are keyed and the male genitalia illustrated.