It is difficult to determine the conservation status of aquatic insects because we lack historical distributions. The Illinois Natural History Survey (INHS) Insect Collection contains 6.5 million specimens suitable to document declines in aquatic species. NatureServe rates stoneflies (Plecoptera) as the third most imperiled taxon in the USA, regardless of habitat. Previous work by DeWalt & others has documented loss of two endemic species and 20 extirpations (totaling 28.6% of 77 species) in Illinois. There, glaciated regions and larger rivers lost most species. Taxonomically, large, predatory, long-lived species in the Perlidae were disproportionately lost. The authors have modeled historic distributions using INHS museum presence/absence data of several perlid species in relation to GIS variables little modified by humans. Negative data were derived from the positive distributions of other species and General Additive and Random Forest models were used to created probabilities of natural occurrence for each species. These were plotted as contoured GIS maps and the models tested using contemporary collections of each species. These models are applicable to predict historic distributions of other aquatic species.