Cottage Lake is a census-designated place in King County, Washington, United States. The population was 22,494 at the 2010 census. The lake itself falls within the 98072 ZIP code, while the developments east of the lake fall under the 98077 ZIP code. Based on per capita income, Cottage Lake ranks 13th of 522 areas in the state of Washington to be ranked. Coldwell Banker ranked Cottage Lake#1 in 2013 for the fastest growing suburb in America.