The biological diversity reflected by nearly 300,000 caddisfly specimens collected throughout Minnesota since 1985 was compared with that of 25,000 specimens recorded prior to 1950 and was analyzed based on the 5 caddisfly regions of Minnesota. In the Lake Superior, Northern, and Southeastern regions, >90% of species known historically from each region were recovered and additional species were discovered. In the Northwestern and Southern regions—the most disturbed areas of Minnesota—species recovery ranged from 60 to 70%. Historical and contemporary assemblages were similar to each other in the former 3 regions and markedly different in the latter 2. Prior to 1950, species in all trophic functional groups were widespread in all regions. A similar pattern still exists in the Lake Superior, Northern, and Southeastern regions, whereas the Northwestern and Southern regions are now dominated by filtering collectors in all sizes of lakes and streams. Over 65% of species extirpated from any region were in the long-lived families Limnephilidae and Phryganeidae, and 70% of these same species were in the shredder functional group. Almost 30% of the statewide fauna has been found from <5 localities since 1950, suggesting a degree of imperilment on par with that of freshwater bivalves, gastropods, and fish. These observed losses of biodiversity and changes in trophic composition have probably occurred as a result of anthropogenic disturbance throughout most of the northcentral US.