Descriptions are provided for larvae of nine species of Ceratophyllus Curtis for which swallows in North America, north of Mexico, are recorded hosts. A detailed description is provided for the larva of Ceratophyllus celsus celsus Jordan and for other species only where there are significant differences from C. c. celsus. Ceratophyllus celsus celsus, Ceratophyllus scopulorum Holland, and Ceratophyllus petrochelidoni Wagner are characterized by a large number of anal comb (25–42) and anal mound (13–23) setae, but among themselves have not proved separable; Ceratophyllus styx riparius Jordan and Rothschild is remarkable in having two ventral plate setae on all thoracic segments as well as on the eighth and occasionally the ninth abdominal segments; Ceratophyllus idius Jordan and Rothschild and Ceratophyllus niger C. Fox characteristically display stout ventral plate setae on the thoracic segments, as seen in C. c. celsus, but have fewer anal comb and mound setae. We are unable to separate larvae of C. idius and C. niger from each other. Ceratophyllus gallinae (Schrank) also has few comb and mound setae, but the ventral plate setae are more slender than evident in other species treated here. Ceratophyllus diffinis Jordan and Ceratophyllus garei Rothschild, the sole Nearctic representatives of the subgenus Emmareus Smit, are characterized by their short, slender, thoracic ventral plate setae, but have not been separated from each other here. Redescriptions are provided for larvae of C. gallinae and C. garei. Descriptions for all other taxa are provided for the first time. A key is provided to the known larvae of species associated with swallows in North America, north of Mexico.