Koga is a city located in Fukuoka Prefecture, Japan. As of 29 February 2024, the city had an estimated population of 59,282 in 26981 house…Koga is a city located in Fukuoka Prefecture, Japan. As of 29 February 2024, the city had an estimated population of 59,282 in 26981 households, and a population density of 1400 persons per km². The total area of the city is 42.07 km².