Nakatsu is a city on the northern border of Ōita Prefecture in Kyushu, Japan. As of 31 October 2023, the city had an estimated population of 82,301 in 41222 households, and a population density of 96 persons per km2. The total area of the city is 491.53 km2 (189.78 sq mi).

Ōita Prefecture is a prefecture of Japan located on the island of Kyūshū. Ōita Prefecture has a population of 1,136,245 and has a geographic area of 6,340 km2. Ōita Prefecture borders Fukuoka Prefecture to the northwest, Kumamoto Prefecture to the southwest, and Miyazaki Prefecture to the south.