The tributaries of the Namoi rise in the Liverpool Ranges in the south, the Great Dividing Range in the east and the Nandewar Range to the north.

The main towns located within the Namoi include Barraba, Manilla, Nundle, Tamworth, Quirindi, Werris Creek, Gunnedah, Narrabri and Walgett. The Catchment includes either all or parts of 14 local government areas.