Shimōsa Province was a province of Japan in the area of modern Chiba Prefecture and Ibaraki Prefecture as well as the bordering parts of Saitama Prefecture and Tokyo. It lies to the north of the Bōsō Peninsula (房総半島), whose name takes its first kanji from the name of Awa Province and its second from Kazusa and Shimōsa Provinces. Its abbreviated form name was Sōshū (総州) or Hokusō (北総).

Chiba Prefecture is a prefecture of Japan located in the Kantō region of Honshu. Chiba Prefecture has a population of 6,278,060 and has a geographic area of 5,157 km2 (1,991 sq mi). Chiba Prefecture borders Ibaraki Prefecture to the north, Saitama Prefecture to the northwest, and Tokyo to the west.