The endohelminth component communities of creek chub (Semotilus atromaculatus) were studied in southeastern Nebraska to determine whether parasite community similarity corresponded to drainage identity. Creek chub were sampled from 12 sites on 3 drainages of the Big Nemaha River system during 4 periods from summer 2003 to summer 2005. Analysis of similarity, cluster analyses, and ordination suggested that community similarity was more similar among sites within drainages than among drainages. Vector analysis and indicator species analysis demonstrated that the distributions of 2 of the parasite species, Paulisentis missouriensis (Acanthocephala) and Rhabdochona canadensis (Nematoda), were highly aggregated among drainages. Allocreadium lobatum (Trematoda) and Proteocephalus sp. (Cestoda) occurred more uniformly among sites and drainages. Procrustean analyses suggested that drainage-level differences in species composition better explained the spatial pattern of community similarity than did physical distance. These results suggest that there are predictable differences in component communities among drainages.