5 airports in Seattle? There is the main airport: SeaTac, Boeing field which is mostly private aircraft, Paine Field which just started commercial flights (45 minutes from Seattle), and Bellingham (1 1/2 hours from Seattle which doesn’t seem like it should count as it is closer to Vancouver, BC). Even with the stretch, how are there 5?
These numbers are based on the Wikipedia page, and some of the airports can be as far as 100+ kilometers away from the city itself. They are still counted for the city if they mainly serve that city/have been built for that city. And it isn't always simple to determine.