Because the race scheme for Heterodera glycines was expanded recently from 5 to 16 races, the occurrence and distribution of races in Illinois need clarification. Forty-four populations of H. glycines were collected from sites in 23 of the 88 infested counties. Populations were tested using the differential soybean lines Pickett 71, Peking, PI 88788, and PI 90763. Lee 68 and Williams 82 were used as standards. Seedlings were grown in 7.5-cm-d clay pots and inoculated with 1,000 eggs and second-stage juveniles obtained from H. glycines-infested field soil. Plants were maintained in a greenhouse at 22-28 C. After 1 month, the number of first-generation white females that developed on each differential was determined and the race of the population was designated. Twenty-eight populations were race 3, twelve were race 1, two were race 5, one was race 2, and one was race 4. Populations of races 3 and 1 were widely distributed in the state. In 26 of the 28 race determinations, race designations using Williams 82 and Lee 68 were the same, indicating that if Lee 68 is not available, Williams 82 may be a suitable alternative for race tests done in the north central United States.