Koga (古賀市, Koga-shi) is a city located in Fukuoka Prefecture, Japan. It is northeast of Fukuoka City. The city was founded on October 1, 1997.
The city has an estimated population of 59,645 and a population density of about 1,400 persons per km². The total area is 42.07 km².
Koga Station is on the Kagoshima main line.