Seattle is the largest city in Washington, United States. From sometime until 1999, a cult led by the Goa'uld System Lord Seth operated north of the city, until it was foiled by SG-1, and Seth was killed. (SG1: "Seth")
In 2001, Adrian Conrad stayed in an abandoned hospital in Seattle.
In 2004, Alec Colson almost died at SeaTac airport when his plane was sabotaged.
In 2005, Ba'al, who wished to seek refuge on Earth, had a building constructed in Seattle, which was laced with Naquadah. The building, would devastate anything in at least a five mile radius if it were to explode. Ba'al planted the bomb there as insurance should Stargate Command and the Free Jaffa Nation continue to stop him. Fortunately, the Prometheus transported the building to space before that could happen. (SG1: "Ex Deus Machina")
In 2009, Lt. Tamara Johansen originally wanted to leave the Air Force for a University in Seattle, after her scholarship went through. However, that could not be possible, as before she could resign, Icarus Base fell under attack, and she and around 80 other people evacuated to the Destiny. (SGU: "Air, Part 2")