WEBYamaguchi Prefecture (山口県, Yamaguchi-ken) is a prefecture of Japan located in the Chūgoku region of Honshu. Yamaguchi Prefecture has a population of 1,377,631 (1 February 2018) and has a geographic area of 6,112 km 2 (2,359 sq mi).Yamaguchi Prefecture borders Shimane Prefecture to the north and Hiroshima Prefecture to the northeast.. Yamaguchi is the capital and Shimonoseki is the ...