[1][2] The Bōsō Peninsula is defined by the Pacific Ocean to its east and south, Tokyo Bay to the west, and the Edo and Tone rivers to the north.

[3] Mount Atago in Minamibōsō and Kamogawa is the highest point on the peninsula with an altitude of 408.2 m (1,339 ft).

The Shimōsa Plateau and the coastal lowlands and interior river valleys are chiefly used for rice cultivation.

[2] The peninsula gets its name and kanji from the former provinces that were located there: Awa (安房), Kazusa (上総) and Shimōsa (下総).

The Japan Meteorological Agency refers to the west and east coasts of the peninsula as Uchibō (内房) and Sotobō (外房) respectively.