Shimonoseki is a city located in Yamaguchi Prefecture, Japan. As of 30 June 2023, the city had an estimated population of 248,193 in 128762 households and a population density of 350 persons per km2. The total area of the city is 716.18 square kilometres (276.52 sq mi). It is the largest city in Yamaguchi Prefecture and the fifth-largest city in the Chūgoku region in terms of population. It is nicknamed the "Fugu Capital" for the locally caught pufferfish, and is the largest harvester of the pufferfish in Japan.

Yamaguchi Prefecture is a prefecture of Japan located in the Chūgoku region of Honshu. Yamaguchi Prefecture has a population of 1,377,631 and has a geographic area of 6,112 km2. Yamaguchi Prefecture borders Shimane Prefecture to the north and Hiroshima Prefecture to the northeast.