Biogeographical processes have had lasting impacts on current species assemblages at regional and local scales, affecting taxonomic, functional, and phylogenetic diversity. In this study, we examined patterns of richness and body size of the aquatic insect order Trichoptera (caddisflies) across the United States and Canada using the Trichoptera Nearctica distributional checklist and specimen data from the Global Biodiversity Information Facility. Geographic regions show varying compositions of families: five families remain constant as the most speciose, though in different proportions. Focusing on Hydroptilidae, Hydropsychidae, Leptoceridae, Rhyacophilidae, and Limnephilidae, we analyzed the relationships of wing length and species richness with geography (latitude, longitude, elevation), climate (contemporary and Pleistocene), and habitat (total water area). We found that size increased in the north and west of the US and Canada, driven by the distribution of Hydroptilidae in the south and east and Limnephilidae in the west. Surprisingly, longitude was a more influential factor than latitude for four out of the five families. Other important variables for families included elevation and paleoclimate variables. The combinations and varying directions of geography and paleoclimate variables point to potential family-dependent influences on Trichoptera in an historical context; this information may aid in understanding the implications of current and future climate change and the potential for range shifts.