Members of the genus Trachelomonas comprise a portion of the Euglenophyta which have received only minor attention in the state of Illinois despite their wide distribution. Britton, in his A Catalog of Illinois Algae (1944), reports 11 species recorded from 33 different counties. Tiffany and Britton indicate the same species in The Algae of Illinois (1952). Two of the most extensive accounts (Prescott, 1951; Forest, 1954) of species of Trachelomonas in the midwestern United States together list well over sixty species and varieties. Recent preliminary investigations in the southern counties of Illinois revealed a large number of species heretofore unrecognized in the state. One such investigation to which the following text is devoted disclosed 31 species and varieties from a single area in a southern county, 26 of which can be considered new records for the state.