The Seattle and Walla Walla Railroad was a 3 ft narrow gauge railroad and was the first proper railroad to serve Seattle, Washington, preceded only by horse-drawn rail vehicles and by a coal train making the very short haul from Lake Union to Pike Street. Despite its ambitious name, actual construction never went beyond King County, the county of which Seattle itself is the seat. After being sold to Henry Villard's Oregon Improvement Company in 1880 it was renamed the Columbia and Puget Sound Railroad. In 1916, that became the Pacific Coast Railroad Company.

King County is located in the U.S. state of Washington. The population was 2,269,675 in the 2020 census, making it the most populous county in Washington, and the 12th-most populous in the United States. The county seat is Seattle, also the state's most populous city.