İzmit (Greek: Νικομήδεια, Nicomedia) Izmit is not to be confused with Izmir Izmit is a city in Turkey, administrative center of Kocaeli Province as well as the Kocaeli Metropolitan Municipality. It is located at the Gulf of İzmit (the ancient Gulf of Astacus) in the Sea of Marmara, about 100 km (62 mi) east of Istanbul, on the northwestern part of Anatolia. The city center has a population of 300,611 (2011 census). The population of the province (including rural areas) is 1,459,772 (Unlike other provinces in Turkey apart from Istanbul, the whole province is now included within the municipality of the metropolitan center.)