Washington region’s growth driven primarily by adults, census data shows

The census showed record growth in the Greater Washington region between 2010 and 2020, ballooning from 5.6 to 6.4 million people, according to a new report from Urban Institute fellow Peter Tatian.

Most of that population growth came from adding new adults — the region added 639,000 adults in that decade, a 15% increase. Meanwhile, the population of children under 18 grew by only 7%, or 96,700. For every additional child, the region added about five adults.

The District, which saw similar trends to the region, has a larger share of adults in its population than any state, according to census data. A full 83.4% of DC residents were over 18 in 2020, compared to 77.9% of the US at large.

But the region’s Maryland counties were the ones with the most growth in their adult populations, adding 12 adults for every child. Maryland population growth was driven by increases in the Hispanic/Latinx, Black, and Asian and Pacific Islander populations.

The share of adults in the US population is growing too, according to the Census Bureau, a combination of aging Baby Boomers and a decrease in fertility since 2007. And unlike in the Washington region, the overall number of children in the US at large actually declined between 2010 and 2020 by 1.4%.

Although the District has a greater share of adults than any state, those adults are young — in fact, in 2019, only one state, Utah, had a younger median age. The median DC resident in 2020 was 34 years old.