The latest migration data from the Internal Revenue Service reveals that King County continued to gain residents from other states — but those gains are more than offset by losses to other Washington counties.
By tracking the addresses on tax returns from one year to the next, the IRS data offers a highly accurate picture of domestic migration, along with insight into the wealth of migrating populations through the flow of total adjusted gross income (AGI).
The great majority of U.S. adults file a tax return. A 2020 analysis by the nonpartisan Tax Policy Center found 82% of single adults and married couples who could file a tax return did so.
The data's main drawback is the lag: the latest release covers the 2022 to 2023 tax years, while the U.S. Census Bureau's most recent population estimates cover 2024 to 2025.
First, the big picture. King County experienced a loss of residents due to domestic migration. Between 2022 and 2023, roughly 105,000 people moved out of the county to other U.S. counties, while about 92,000 moved in — a net loss of roughly 13,000 residents.
They took their paychecks with them. Outbound migrants carried about $8.7 billion in AGI out of King County, while incoming residents brought in $6.7 billion — a net drain of nearly $2 billion from the local economy in a single year, just from people relocating.
But despite all the talk of people fleeing Northern states for the Sunbelt, the data here doesn't show that. King County's population loss wasn't driven by a mass exodus to Texas, Florida or Arizona — it was happening right in our own backyard.
About 47,800 people left King County for another Washington county, while only 30,200 moved in from elsewhere in the state — a net loss of about 17,600.
Neighboring counties absorbed the vast majority of those departures. Pierce County handed King its largest net loss. It took in more than 16,200 people while sending back just 9,500 — a difference of about 6,700 movers in favor of Pierce. Snohomish County was close behind, gaining more than 17,200 from King while sending about 11,000 the other way, handing King a net loss of about 6,200. Kitsap and Thurston counties also had significant population gains at King County's expense — net differences of 900 and 500 movers, respectively.
That pattern points to a housing affordability and cost-of-living problem. These residents aren't leaving the region — many are simply being priced out of King County.
Subtract those in-state moves, though, and the story flips: King County actually gained population from the rest of the country. Roughly 62,000 people moved here from other states, compared with more than 57,000 who left for other states — a net gain of nearly 5,000 residents from outside Washington.
Los Angeles County was one of the biggest sources of that gain, sending King County more than 3,100 people while taking back only about 2,400 — a net gain of more than 700, the largest from any single county. Honolulu County ranked second, with a net gain of about 390, followed by Alameda County — home to Oakland — with a net gain of about 360.
Of course, King County lost residents to some out-of-state destinations, too. Maricopa County, Arizona, home to Phoenix, drew the most former King County residents of any county outside Washington — about 2,460 — while roughly 1,800 people moved the other way, for a net loss of more than 600. That's King County's largest net loss to any single out-of-state county.
The second-largest out-of-state loss was to a New York County — Manhattan — at about 450 people. Williamson County, Texas, in the Austin metro area, was third, with a net loss of about 360.
One more wrinkle in the data may give local policymakers pause. Despite gaining more people from other states than it lost to them, King County still saw a net loss of $446 million in AGI to out-of-state migrants. In other words, the people leaving Washington for other states had, on average, higher incomes than the ones moving in.
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