The aim of this study was to determine whether geographic variation exists in the composition of note types in the chick-a-dee call of Carolina chickadees. This determination is of interest for two reasons: earlier studies with a related species suggested minimal geographic variation in note composition, and geographic variation in social signals may represent important developmental or selection processes shaping signal use. Carolina chickadees were recorded in a naturalistic observation study in west-central Indiana. Chick-a-dee calls were analyzed and compared to calls from an eastern Tennessee population that had been described in a previously published study (Auk, 125, 2008, 896). Despite much similarity in the basic rules by which notes are organized to compose calls, there were several significant differences in how calls of the two populations were structured. Furthermore, birds from Indiana used their chick-a-dee calls in certain contexts in different ways compared to birds from Tennessee. These findings suggest interesting population-level variation in this call system, and future research should be able to determine whether these differences are driven by evolutionary, ecological, or developmental factors, or some combination of these factors.