correction
The headline accompanying a previous version of this article incorrectly stated that most U.S. counties lost population in 2020. Most counties reported more deaths than births. The article has been corrected.
Johnson said he expected the data to show a natural decrease but was surprised at its scale. Natural decrease occurs when a population records more deaths than births. “I think one of the most important findings is the fact that almost 2,300 counties had more deaths than births in them. That’s unheard of in American history,” he said.
He said the impact of the coronavirus, along with other trends that limited population growth, had created a “perfect storm,” and that one would have to go back at least to the 1918 flu pandemic to find anything like it.
The data also offered statistical backing to widespread anecdotal evidence suggesting that millions of Americans moved out of the largest cities in the nation, including the District, during the pandemic.
Whether for safety from infectious disease or convenience during shutdowns, millions of residents traded cities for suburbs or larger suburbs for smaller ones. Many migrated farther into rural counties or resettled to second homes in vacation areas, such as the Catskill Mountains or the Delmarva Peninsula.
The two largest cities in the nation, Los Angeles and New York, suffered the sharpest losses as a result of internal migration. Los Angeles County lost over 179,750 people in net domestic migration, while New York County lost over 113,640.
California, Oregon and Mississippi had the most counties negatively affected by international migration losses, while Alaska, Louisiana and Illinois had the most counties affected by losses caused by domestic migration within the United States.
Of course, the outflows from some states meant gains in others. Maricopa County in Arizona, which includes Phoenix, received the most people, with more than 46,860 flowing in, from other areas of the United States.
“I’m very surprised by this because I didn’t think it was going to be as dramatic, the domestic migration piece of it,” said William Frey, a senior fellow at the Brookings Institution, who analyzed the data and its impact on the Washington region. “It may be a blip, and I think it is, but it’s certainly noteworthy. I think that’s the bigger demographic pattern here.”
Frey said that although outward domestic migration from these and other major cities had been underway for many years, its effect had been masked by increases in foreign immigrants, but those numbers also slowed during the pandemic.
The data released Thursday covered roughly 3,140 counties, more than 380 metropolitan statistical areas and over 540 smaller locales known as micropolitan statistical areas. The period covered by the data, July 2020 to July 2021, also coincided with some of the peak rates of the spread of the coronavirus, as reflected in reported cases.
In that time, nearly 75 percent of all U.S. counties experienced a natural population decrease, compared with 55 percent of all counties in 2020 and 45 percent in 2019, the Census Bureau found. In Maine, Delaware, Rhode Island and New Hampshire, the natural population decrease occurred in every county.
The District recorded a loss of 20,040 people, driven mostly by domestic migration, while the Washington metropolitan area lost more than 29,000 people, Frey said. Montgomery County experienced a loss of more than 6,410 people, Prince George’s County reported a decline of nearly 10,300, and Fairfax County’s population declined by over 8,750. Prince William County added more than 1,730 people, Frey found.
He also noted the huge turnaround in immigration, tracing a peak influx of more than 47,000 reported in July 2015 to only 12,600 last year.