King County had decade’s third-largest population growth among U.S. counties

Let this sink in: In the past decade, King County added more people than 34 of the 50 U.S. states.

The U.S. Census Bureau released 2019 data last week for all U.S. counties, which allows us to take a look at population trends for the complete decade. It shows King County gained about 321,000 people. Only two counties had a larger numeric gain in the 2010s: Maricopa in Arizona (Phoenix) and Harris in Texas (Houston).

That 321,000 is a net increase — in other words, the number of people who moved in or were born here minus the number who moved away or died.

While the rest of the country grows in the sun, we prove you can also grow in the rain.

Among the 10 U.S. counties with largest gains in population, King is the only one not located in the Sun Belt. Six of the top 10 are in Texas. Other than Washington and Arizona, Nevada’s Clark County (Las Vegas) and California’s Riverside are also among the 10.

King County’s total population on July 1, 2019, was about 2,253,000. While we remain the 13th largest county in the nation, we’re only about 1,000 people behind the 12th largest county, Queens, New York (New York City’s five boroughs are also U.S. counties). King should overtake Queens next year, assuming current population trends continue.

Most of the nation’s heavily populated urban counties, like King, saw growth over the course of the decade. But many rural counties have been shrinking. Overall, of the 3,142 counties in the nation, 1,683 (54%) have lost population since 2010. That’s mainly because immigration is down sharply, combined with a low birthrate.

“One interesting trend we have seen this decade is widespread population decline among smaller counties, while larger counties tended to have population growth,” said Dr. Christine Hartley, a demographer in the Census Bureau’s Population Division, in a news release.

There are a few exceptions among large counties, most notably Cook County, Illinois (Chicago), and Wayne County, Michigan (Detroit), which both suffered population losses.

Of course, the 2019 data captures a period before the novel coronavirus crisis hit. The White House coronavirus task force estimates between 100,000 and 240,000 deaths from the virus, with mitigation. In 2019, there were about 242,000 more births than deaths nationwide. So it’s possible in 2020, because of fatalities from the coronavirus, there could be more deaths than births in the United States.

Population losses in the past decade were most heavily concentrated in counties in the Northeast, Midwest and Deep South. Four states registered population declines: Illinois had the heaviest loss, followed by West Virginia, Connecticut and Vermont.

But along the West Coast, most counties saw growth. In Washington, only two counties lost people from 2010 to 2019: Columbia and Garfield, both rural counties in the southwest corner of the state.

Meanwhile, the Seattle area’s influence in the state is increasing. Nearly half (48%) of Washington’s total population growth in the last decade came just from King and Snohomish counties.

Even though King County continues to register strong growth, the last couple of years have shown a cooling off. In the middle of the decade, we were seeing increases of more than 40,000 per year. For the last couple of years, it has been a little less than 25,000.

International immigration was the primary driver of King County’s massive population growth last decade, bringing in a net increase of 161,000 people. Next was “natural increase,” which is the number of births minus the number of deaths. That added about 115,000. Finally, we gained another 46,000 from net domestic migration (people moving into the county, minus those moving away, from within the U.S.).

As for that last number, King County is one of the few large counties to gain population from elsewhere in the U.S. Among the 15 most populous counties, the only other two were Maricopa, Arizona (Phoenix), and Tarrant, Texas (Fort Worth).

But as the cost of living here continues to rise, that trend appears to have reversed. In both 2018 and 2019, nearly 5,000 more people left King County for other parts of the U.S. than moved in.