Several species of western North American chipmunks (Rodentia: Tamias) are distributed in overlapping ranges. Field-collected specimens of 9 species of chipmunks from 8 U.S. states were examined externally for fleas (Siphonaptera). We document flea infestations and 1 new range extension. This work demonstrates that ongoing field collection can shed light on host and parasite distributions over large geographical areas.