Tachiarai is a town located in Mii District, Fukuoka Prefecture, Japan. As of 31 January 2024, the town had an estimated population of 16,065 in 6283 households, and a population density of 700 persons per km². The total area of the town is 22.84 km2 (8.82 sq mi).

Fukuoka Prefecture is a prefecture of Japan located on the island of Kyūshū. Fukuoka Prefecture has a population of 5,109,323 and has a geographic area of 4,986 km2. Fukuoka Prefecture borders Saga Prefecture to the southwest, Kumamoto Prefecture to the south, and Ōita Prefecture to the southeast.