The Kootenays have no official boundaries and the usual definition of the region is the drainage basin of the lower Kootenay River near Creston, through to its joining with the Columbia River at Castlegar . In most interpretations of the Kootenay Region, also included are an area to the east which encompasses the upper drainage basin of the Kootenay Rive , a region spanning from the Purcell Mountains to the Alberta border, and includes Rocky Mountain cities such as Cranbrook and Kimberleyand the southern Canadian Rockies in and around Fernie plus the Salmo River basin which adds the communities of Rossland, Trail, Fruitvale and Salmo.

Some or all of the following areas to the north, which drain into the Columbia River, are also commonly included in the Kootenays: The Arrow Lakes area, which adds Nakusp. The Upper Columbia Valley, which parallels the first section of the Kootenay River, including the communities of Invermere and Radium Hot Springs.