Kocaeli, due to its geographical location, before and after the conquest of İstanbul, had been an important administrative unit. Administrative centers to which Kocaeli was connected changed over the years. Development and diversification of transportation facilities in the region led to a frequent change of administrative units to which Kocaeli was connected. Ultimately, this gave Kocaeli a detached administration status. Indeed, Kocaeli, which was connected to Kastamonu, Hüdâvendigâr and İstanbul in the 19th century, became a detached administrative center in 1887. The status of Kocaeli as a detached administration continued until it was converted into a province in 1923