Reproductive characteristics and the age-body size relationship of female Chrysemys picta marginata were studied at Miller's Marsh on Beaver Island, Michigan. Environmental influences on reproduction were evident in that turtles nested relatively early when the previous spring (April and May) temperatures were relatively warm. Clutch wet mass (CWM), clutch size (CS), and egg wet mass (EWM) were all correlated with maternal carapace length (CL). Over six activity seasons, significant annual variations in EWM and CS occurred, but these variations were not related to temperature or precipitation patterns of the current or previous year. Therefore, it seems unlikely that annual variation in EWM represents proximate variation or adaptive phenotypic plasticity where offspring size might be adjusted to meet predictable temporal changes in offspring growing and survival conditions. Annual variation in CS was mainly caused by slight variations in mean maternal CL. When compared to previously published studies on C. p. marginata populations from southern Michigan, Miller's Marsh turtles were larger in CL, produced large EWM and small CS relative to maternal body size, and apparently delayed sexual maturation, which would have resulted in relatively large maternal CL (and therefore EWM and CS) at primiparity and thereafter.