A study of the fish faunas in all or parts of seven Illinois river basins revealed an average loss of 8.4 species per basin over approximately the last 100 y. In contrast, between the 1980s and 1990s, five basins showed an increase in the species richness (number of species) and two showed a statistically significant increase (paired t-test) in the species richness per sample site. Only the Kaskaskia River basin had a significant decline (paired t-test) in the species richness per sample site between the 1980s and 1990s. Minnows (Cyprinidae) had the largest number of species showing declines over the last 100 y and was followed in decreasing order by darters and perches (Percidae), catfishes (Ictaluridae), suckers (Catostomidae), topminnows (Fundulidae) and sunfishes (Centrarchidae). Changes in the overall fauna since the 1980s show an increase in species occurrence, but minnows and catfishes showed little net change and suckers, sunfishes and darters showed a positive increase in occurrence.