The province is located at the easternmost end of the Sea of Marmara around the Gulf of İzmit.

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.

Kocaeli has an airport named Cengiz Topel Naval Air Station which is used for military and civilian transport.

This geographical article about a location in Kocaeli Province, Turkey is a stub.