 According to the United States Census Bureau, the Cottage Lake CDP has a total area of , of which are land and , or 0.55%, are water.Most of the CDP drains south and west to the Sammamish River, while the eastern edge drains to the Snoqualmie River.At the 2000 census there were 24,330 people in 7,772 households, including 6,800 families, in the CDP.