The family name Koga was succeeded from the period of MINAMOTO no Morofusa and has its origin in a villa named Kogasuikaku, located in Koga, Otagi District, Yamashiro Province (today Koga, Fushimi Ward, Kyoto City).
久我という家名は、源師房の代より伝えられ、山城国愛宕郡久我（こが）（現在の京都市伏見区久我）に構えた久我水閣が由来。