Yamaguchi is the capital city of Yamaguchi Prefecture, Japan. As of 1 July 2023, the city had an estimated population of 191,470 in 88,799 hous…Yamaguchi is the capital city of Yamaguchi Prefecture, Japan. As of 1 July 2023, the city had an estimated population of 191,470 in 88,799 households and a population density of 190 persons per km². The total area of the city is 1,023.23 square kilometres.