- Granite Falls is a city in Snohomish County, Washington, United States. It is located between the Pilchuck and Stillaguamish rivers in the western foothills of the Cascade Range, northeast of Lake Stevens and Marysville. The city is named for a waterfall north of downtown on the Stillaguamish River, also accessible via the Mountain Loop Highway. It had a population of 3,364 at the 2010 census.