I studied a metapopulation of Sonoran Mud Turtles ('Kinosternon sonoriense') in the Chiricahua Mountains, Arizona, United States of America. I tested hypotheses related to growth, reproduction, terrestrial habitat use, life history, and demography of turtles and I constructed a life table for my study population. In my study population, turtles experienced delayed maturity, indeterminate growth, a decrease in growth rate at maturity, and a positive relationship between, both, reproductive output and survivorship with female body size. Optimal egg size theory did not explain variation in reproductive output. Sonoran Mud Turtles exhibited life history and demographic characteristics similar to those features in other turtles. In my study population, longevity and iteroparity have likely evolved from high adult survivorship because adult survivorship had the greatest influence on population parameters. Variations in growth and reproduction among subpopulations were correlated to local environmental variation. Sonoran Mud Turtles select microhabitat conditions at terrestrial sites relative to the function of the site.