Foundation of the central municipality of Köseköy goes back to 1600s. However, when we look at the historical artifacts and tombs of the Byzantine and Roman periods that have been discovered during the excavations from time to time, we can say that establishment of Köseköy was long before 1600s and started with Bithynia. During the War of Independence, the Greeks living in the surrounding villages have caused great harm to the town and the inhabitants. At the end of the population exchange between Turkey and Greece in 1925, Köseköy has begun the receive migration because of settlement of the citizens sent from Greece to Turkey and continued to let immigrants from different regions of our country, particularly from the Black Sea Region.
While having a population of around 400 people in the general population census conducted in 1955, Köseköy had a rapid population increase due to establishment and development of rubber factories and other industrial facilities as of 1960 and reached a population of 2000 people in early 70s, therefore, as a result of the referendum for establishing a municipality, it has gained municipal status.
By the Law No. 5747 concerning Establishment of Districts within the Boundaries of Metropolitan Municipalities and Amendment to Certain Laws, which has been published in the Official Gazette no. 26824 dated 22.3.2008 and enacted, legal entities of the first tier municipalities of Uzunçiftlik, Uzuntarla, Eşme, Acısu, Maşukiye, Büyükderbent, Arslanbey, Sarımeşe and Suadiye have been revoked and they joined the First Tier Municipality of Köseköy together with their neighborhoods. Municipality of Köseköy has been the center, Sultaniye, Pazarçayırı, Örnekköy, Karatepe, Balaban, Nusretiye, Şirinsulhiye, Avluburun, Eşme, Ahmediye, Ketenciler villages were affiliated to the center and Köseköy Municipality’s name was changed to Kartepe. Thus, Kartepe district of Kocaeli province was created