Body size, growth, and longevity in Northern Map Turtles (Graptemys geographica) from Dewart Lake in northern Indiana were studied from 1979 to 2016. Based on captures of 214 males (72 recaptures) and 99 females (40 recaptures), we generated von Bertalanffy growth equations which corroborated our growth curves based on counts of plastral growth rings and recaptured turtles. Females diverge from males in their faster growth by the end of their second season. Our oldest females were only 18–20 seasons old, and the oldest males were only 13–15 seasons old, suggesting a short generation time and a possible sexual difference in longevity. For the species, we detected no latitudinal pattern of size or age at maturity but found some support for a latitudinal increase in body size in accordance with Bergmann's Rule.