Its adjacent provinces are Balıkesir to the west, Kütahya to the south, Bilecik and Sakarya to the east, Kocaeli to the northeast and Yalova to the north.
Po I. svetovni vojni je pokrajino dobila Grčija, vendar so jo sile, ki jih je vodil Mustafa Kemal Atatürk priključile Turčiji v vojni za neodvisnost.