Surname Кога (Koga 
, 古河 
, 古家 ) , in all the world, is quite a common family name. The last name Кога is habitual in Paraguay, where it is quite a rare surname, Zimbabwe, and Luxembourg. Not in comparison with a country's population, it is the most numerous in Brazil, the United States, and Japan. Very seldom, Кога is the forename as well as the last name.