Lake Sammamish was an early favorite for the new field since seaplanes were still used on long-range routes, but the nearby Cascades posed a navigational hazard. Tacoma offered the Port $100,000 if the Port would locate the new airport so Tacoma would be well served too. The Port Commission selected a site near Bow Lake, roughly equidistant from Seattle and Tacoma, on March 30, 1942, and dubbed it Seattle Tacoma Airport (the word "International" was added later).
Construction on the original 907-acre tract began on January 2, 1943. The first landing strips were completed in October 1944 at a cost of $4 million, and a modern terminal opened on July 9, 1949.