İzmit is a municipality and the capital district of Kocaeli Province, located in northwestern Anatolia, Turkey. Situated on the Gulf of İzmit in the Sea of Marmara, the city is positioned approximately 100 km east of Istanbul. The area covers 480 km2 and had a population of 376,056 as of 2022.
The city serves as the center of a large urban metro area that includes Kartepe, Başiskele, Körfez, Gölcük, Derince, and Sapanca. This metropolitan region is home to approximately 1.2 million inhabitants out of Kocaeli Province's total population of over 2 million. İzmit is notable for being the most populated city or town in Turkey whose name is not shared with its province.