Last week, the U.S. Census Bureau released age data covering the 2020 – 2025 period, offering a portrait of a graying America.

The findings showed that outside the South, the number of children under 18 is shrinking while the population aged 65 and older is growing across the country.

Washington reflects that pattern clearly. Over the five years, the state’s 65-and-older population grew by 200,000 — a 16% increase. At the same time, the under-18 population declined by 55,000, a 3% drop.

The older-adult population increased in all 39 counties of Washington. The number of children fell in 26 of them.

Because of its size, King County registered the largest numerical shifts in the state. It added 48,000 residents aged 65 and older while losing a net 22,000 children under 18. But when it comes to the pace of change, King County is hardly remarkable.

Its 16% growth in the 65-plus population matches the statewide average exactly. The county’s median age nudged upward from 36.9 in 2020 to 37.5 in 2025, but it remains comparatively young. The real momentum behind Washington’s aging trend is coming from rural and mid-sized counties elsewhere in the state.

Skamania County, in Southwest Washington along the edges of the Portland metro area, saw the fastest percentage growth in its older-adult population — a 24% increase over five years. Kittitas County, home to Ellensburg, and rural Stevens County in Northeastern Washington each recorded a 20% increase in residents 65 and older.

At the other end of the age spectrum, Island County, which includes Whidbey Island, posted the steepest decline in its youth population, with the number of children under 18 dropping by 11%. Jefferson County was close behind, losing 9% of its under-18 residents.

Jefferson County stands out in another way. Long established as a retirement destination, it saw its median age climb from 59.8 to 61.7 between 2020 and 2025 — that places it among the 10 oldest counties by median age in the United States.

Not every county saw its child population shrink, however. A handful bucked the trend, though all the increases were less than 10%.

Pend Oreille County recorded the highest percentage growth in its under-18 population, up 9% — though in this sparsely populated county, that translates to roughly 250 additional children. Lewis County, which includes Centralia, posted the largest numerical increase in the number of children, with a net gain of more than 800.

So what is driving these shifts?

The growth in the 65-plus population is largely a matter of generational timing. Baby boomers — born between 1946 and 1964 — have been aging into retirement for years, and a significant share of that generation crossed the 65 threshold during this period, swelling the older-adult ranks.

The decline in the under-18 population reflects a broader set of societal changes. Birthrates have been falling for years. Adults are marrying later, and many are delaying parenthood or forgoing it altogether. Economic pressures — particularly the cost of housing, childcare and education — are among the factors shaping those decisions.

This new census data offers a snapshot of a state in transition. An aging population will likely reshape housing demand, healthcare needs, school enrollment and the labor market. The shift is gradual, but as the 2025 data makes plain, it is well underway.