We used principal coordinates analysis to analyze variation in 11 plumage characteristics of 1,722 Savannah Sparrows (Passerculus sandwichensis) breeding at 55 different sites from throughout the species' range in Canada, Mexico, and the United States. There is clinal interpopulational variation in size with considerable overlap among localities. Savannah Sparrows resident along the Pacific coast of southern California and Baja California, and those from along the coast of Sinaloa and Sonora (i.e., saltmarsh Savannah Sparrows) differ from those throughout the rest of their range (i.e., non-saltmarsh). Variation among populations of non-saltmarsh Savannah Sparrows was clinal with the exception of those from Sable Island, Nova Scotia, which are consistently more pallid than birds from the adjacent mainland. Western Savannah Sparrows are more pallid than those in the east. The median crown stripe of eastern Savannah Sparrows is distinct, whereas the median crown stripe of western Savannah Sparrows generally is indistinct or narrow. Savannah Sparrows, with the exception of those on Sable Island, are also more pallid in relatively hot and dry areas than in cool mesic sites, following the general prediction of Gloger's Rule. There is clinal variation of saltmarsh populations along the Pacific coast with those in the north being relatively dark in coloration, and with more yellow in the supercilium than those farther south. There is also clinal variation among the populations from the east coast of the Gulf of California with pallid birds in the north, where vegetation is sparse, and darker birds to the south; these coastal birds have indistinct median crown stripes and little yellow in the supercilium.