Well-documented natural history allows for thorough study of a species' ecology and evolution. However, inadequate natural history data hamper such studies for many species. For example, diet plays a major role in the evolution of species and traits, but thorough quantitative dietary information is often lacking for many groups. Garter snakes (Thamnophis) have been used as model organisms for numerous studies, including many focused on feeding ecology and evolution, but these studies lack a thorough compilation of dietary records. To fill the substantial natural history gap, we amassed nearly 10,000 dietary records for 32 of 35 Thamnophis species, from more than 150 sources, and classified each species' dietary repertoire. We categorized 15 of 32 species as generalist predators and 17 of 32 species as specialist predators of varying prey groups, presenting novel dietary classifications for 15 species. Additionally, we investigated the hypothesis that generalist predators have larger body size, a pattern shown in other snake communities and lineages. However, we found no significant relationship between body size and dietary specialization in the genus. Our findings add to the knowledge of natural history, ecology, and evolution of Thamnophis and provide access to the largest dietary record repository for the genus to date.