Seattle is the fastest-growing big city in the country, its population just passed 700,000, and more than 1,000 new people are moving here every week.

But where did they come from? LinkedIn is on the case, you’ll never guess what it found. Oh wait, yes you will, it’s San Francisco.

As part of its annual Workforce Report, LinkedIn looked at hiring and employment trends in 20 major U.S. cities, including Seattle. The study found that for every 10,000 people with a LinkedIn account in the Seattle area, approximately nine people came from the San Francisco Bay Area some time in the last year. The other most frequent sources of migration are the nation’s largest cities, New York, Chicago and Los Angeles.

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