Cumberland County, New South Wales

 is roughly coterminous with the Greater Sydney region of Australia. Its limits (anticlockwise from the north-east) are generally Broken Bay, the Hawkesbury River, the Nepean River, the Cataract River, and some of Wollongong. Adjoining counties in the same order are Northumberland, Hunter, Cook, and Camden.

Seventy per cent of the state's population can be found in just this one county, created in 1788 and until 1804 the only one. (There are now over a hundred.)