The key for Trichoptera can be found in Chapter 10 of the Guide to Aquatic Invertebrates of the Upper Midwest, pages 119-135. Once you have keyed out your insect, you can use the photographs on this website to verify your identification.
Larval Trichoptera resemble caterpillars except Trichoptera lack abdominal prolegs with crochets. Tricoptera can be identified by their short antennae, sclerotized head, sclerotized plates on thoracic segments, soft abdomen, three pairs of segmented legs, and an abdomen that terminates in a long pair of prolegs bearing hooks.
In many taxa, the shape and construction materials of a retreat or case can also be diagnostic. However, in macroinvertebrate samples, the case is sometimes lost and morphological characters must be relied upon.