Kocaeli Province (Turkish: Kocaeli ili, pronounced [kodʒaˈeli]) is a province of Turkey. Its capital is İzmit, which is also sometimes called Kocaeli. The province is the successor of the Ottoman-era Sanjak of Kocaeli. The largest towns in the province are İzmit and Gebze. The traffic code is 41. The province is located at the easternmost end of the Marmara Sea around the Gulf of İzmit. Kocaeli is bordered by the province of Istanbul and the Marmara Sea to the west, the Black Sea to the north, the province of Sakarya to the east, the province of Bursa to the south and the province of Yalova to the southwest. The metropolitan area of Istanbul extends to the Kocaeli-Istanbul provincial border. The size and natural conditions of the Bay of İzmit allow for extensive port facilities, including the Gölcük Naval Base. The province is called the industrial capital of Turkey. Kocaeli has an airport named Cengiz Topel Naval Air Station which is used for military and civilian transport. Kocaeli has two universities: Kocaeli University and Gebze Technical University.

Kocaeli, 2 September 1993 issued decree No. 504 won the title with a greater force of law. In 2004, the boundaries of metropolitan municipalities with laws issued in 5216 was the provincial administrative boundaries.

Kocaeli; Istanbul Archaeology and Ethnography Museum, Kasr-i Humayun’s Palace Museum, Izmit Electronic City Museum, Osman Hamdi Bey House and Museum, Museum Ship USS Eversole and a TCG Hizirreis Museum.   Also; Gültepe Necropolis Area, Uctepeler large tumulus and Fatih Sultan Mehmet Otag the ruins are also in the province.

Structure as of Kocaeli province, rich Turkish cuisine a rich variety of restaurants from every region.

Kocaeli province, 41 here, Arastapark Gebze Center, Ncity, Outlet Center, such as the Symbol has a large shopping center.