Understanding growth of the Japanese pond turtle Mauremys japonica in relation to their habitats is crucial in the strategic planning of conservation measures for the species. However, the pertinent baseline data are inadequate. Hence, I sought to investigate geographic variation in the growth rates of M. japonica in the flatland and foothill regions of Chiba Prefecture, Japan. Turtles were captured and recaptured in both regions from 2014 to 2018, and their growth patterns were analyzed using the von Bertalanffy growth curve. The results show that female turtles in the flatlands grew more rapidly than did those in the foothill site. Male turtles showed the same results, but the overall body size of those in the flatlands was larger than those in the mountains. These findings indicate that the flatland region is an essential habitat for the turtles, and that this study may contribute to the conservation of the species, which is already at risk of local extirpation due to multiple anthropogenic threats in the area.