Shoreline is a city in King County, Washington, United States, 9 miles north of Downtown Seattle bordering the northern Seattle city limits. As of the 2010 census, the population was 53,007, making it the 20th largest city in the state of Washington. Based on per capita income, one of the more reliable measures of affluence, Shoreline ranks 91st of 522 areas in the state of Washington to be ranked.