Cook County was one of the original Nineteen Counties in New South Wales and is now one of the 141 Cadastral divisions of New South Wales. It includes the area to the west of Sydney in the Blue Mountains, between the Colo River in the north, and the Coxs River in the south and west, encompassing Lithgow, Mount Victoria, Katoomba, Wentworth Falls, Lawson and most of the other towns in the Blue Mountains. The Nepean River is the border to the east.