Larval taxonomy of caddisflies (Trichoptera) lags behind that of adults. Taxonomic knowledge of Nearctic representatives of Polycentropus Curtis, 1835 (Polycentropodidae) is particularly poorly resolved with the larva of only one of 30 species described and with no western Nearctic larvae known. Herein, the late-instar larvae of four of seven western Nearctic Polycentropus species are described and figured for the first time. A diagnostic matrix to assist in their identification is provided, new state records are reported, and previous records clarified. Issues regarding existing keys for larval Polycentropus sensu lato (i.e., Holocentropus McLachlan, 1878, Plectrocnemia Stephens, 1836, and Polycentropus) are discussed in light of new findings.