The diamond-backed terrapin (Malaclemys terrapin) is the only North American turtle species specialized for living in brackish and saltmarsh environments. The Texas subspecies (Malaclemys terrapin littoralis) is found along most of the Texas Gulf Coast. Previous studies on the prey and diets of Atlantic and Florida subspecies found that the diet of terrapins primarily consisted of crustacean and molluscan species, although differences in dietary composition were observed between the sexes. Furthermore, prey availability had little effect on terrapin distribution within a marsh. We examined the prey availability and diet of Texas diamond-backed terrapins. Comparisons of random locations to terrapin capture locations indicated that prey availability is not a limiting factor affecting terrapin distribution in Texas marshes, but multiple significant seasonal and locational differences in prey were detected at capture sites. Fecal analysis, using multiple metrics, indicated Gastropoda and Decapoda as major components of the diets of Texas terrapins. Plicate horn snails (Cerithidea pliculosa) and fiddler crabs (Uca spp.) were important prey items for all terrapins. There were significant differences between the diets of male and female terrapins, among seasonal diets, and among diets of terrapins captured at different marsh sites. Our prey availability findings support previous studies, but results from fecal analysis indicate a slightly different diet for terrapins than previously reported in other studies. The combined results extend the basic knowledge and understanding of terrapin diets, which will be useful for ongoing conservation and management of M. terrapin, especially the Texas subspecies.