More than 73% of U.S. counties, including Warren County, experienced natural decrease in 2021, up from 45.5% in 2019 and 55.5% in 2020, according to the U.S. Census Bureau’s Vintage 2021 estimates of population and components of change released Thursday.

Natural decrease occurs when there are more deaths than births in a population over a given time period. In 2021, fewer births, an aging population and increased mortality – intensified by the COVID-19 pandemic-contributed to a rise in natural decrease.

Figures released Thursday morning showed Warren County, Pa., noted a reduction of 212 residents for the same time period from July 1, 2020 to July 1, 2021. Its population now stands at 38,134 — down 1.2% from 2020’s number of 38,587. Chautauqua County, listed under the micropolitan of Jamestown-Dunkirk-Fredonia, revealed a natural decrease of 434 residents. According to the 2021 Census, there are 126,807 residents there, a decrease of 850 residents — or 0.7% from 2020.

Most of the nation’s counties – 2,063 or 65.6% — experienced positive domestic migration overall from 2020 to 2021. Arizona’s Maricopa County gained the most (46,866) residents from domestic migration, followed by Riverside County, California (31,251), and Collin County, Texas (30,191). Los Angeles County, California, experienced the greatest net domestic migration loss (179,757 residents), followed by New York County, New York (113,642).

“The patterns we’ve observed in domestic migration shifted in 2021,” said Dr. Christine Hartley, assistant division chief for estimates and projections in the Census Bureau’s Population Division. “Even though over time we’ve seen a higher number of counties with natural decrease and net international migration continuing to decline, in the past year, the contribution of domestic migration counteracted these trends so there were actually more counties growing than losing population.”

In many cases, there was a shift from larger, more populous counties to medium and smaller ones. These patterns contributed to population increases in 1,822 counties (58.0%), while 1,313 (41.8%) lost residents, and eight (0.3%) saw no change in population.

U.S. micro areas, up 0.2% between 2020 and 2021, grew slightly faster than U.S. metro areas, which increased by 0.1%. This is a departure from past trends when metro areas typically grew at a faster rate than micro areas. Among metro areas, 251 (65%) experienced population increases between 2020 and 2021. Of the 543 U.S. micro areas, 287 (52.9%) had population increases in 2021.