Yamaguchi (yämäˈgōchē) [key], city (1990 pop. 129,461), capital of Yamaguchi prefecture, SW Honshu, Japan. A great castle city from the 14th to 16th cent. and the site of many Buddhist temples and a mission established (1550) by St. Francis Xavier, it is now a commercial center. Yamaguchi prefecture (1990 pop. 1,556,286), 2,359 sq mi (6,110 sq km), has good lumber and agricultural resources, and fishing and stock-raising are important. Other industries include iron, steel, and coal.