Seattle has 725,000 residents now according to the Seattle Times: https://www.seattletimes.com/seattl...est-growing-big-city-in-all-of-united-states/
This is an increase of 114,000 in Seattle since 2010. All other cities in King County increased just by 15,000 or 1%.
But if you add up ALL the growth (not just to Seattle and King County), the whole area has gone up. Even Skagit and Whatcom counties have grown significantly and there's development everywhere. Most of the newer folks in Mount Vernon commute to Seattle because they can't even find housing, to say nothing of affordable, in Seattle. But with gas prices now almost back at recession levels, the dynamics may shift in another direction pretty soon...