The age structure of a population can reveal trends in growth and maturation and be used to describe other demographic processes. Accurate descriptions of age structure for populations of snakes are rare, limiting our ability to understand their population dynamics. In this study, I used skeletochronology to determine the age of individuals, and examined the relationship between age and size, in a population of western terrestrial garter snakes (Thamnophis elegans). Most of the adult snakes had between two and six growth layers, and the youngest gravid female had three growth layers. Although lengths and number of growth layers were positively correlated, it would not be possible to predict the age of an individual from its length.