- Shoreline is a city in King County, Washington, United States. It is located between the city limits of Seattle and the Snohomish County border, approximately 9 miles (14 km) north of Downtown Seattle. As of the 2020 census, the population of Shoreline was 58,608, making it the 22nd largest city in the state. 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.