Okutama has an area of 225.63 km2. Mount Kumotori, Tokyo's highest peak at 2017 m, divides Okutama from the Okuchichibu region of the neighboring Saitama and Yamanashi Prefectures. Tokyo's northernmost and westernmost points lie in Okutama, as does Lake Okutama, an important source of water for Tokyo, located above the Ogōchi Dam in the town.