The U.S. population will peak later this century before experiencing a decline by 2100, the U.S. Census Bureau said this week, with low fertility numbers partly explaining the projected decrease. 

The bureau said in a press release on Thursday that the country’s population “is projected to reach a high of nearly 370 million in 2080 before edging downward to 366 million in 2100.” 

The total increase in population from 2022 to 2100 is expected to be only 9.7%, the bureau said. 

Sandra Johnson, a demographer at the Census Bureau, said in the press release that the last five years have seen “notable shifts in the components of population change” in the U.S. 

“Some of these, like the increases in mortality caused by the COVID-19 pandemic, are expected to be short-term,” Johnson said, “while others, including the declines in fertility that have persisted for decades, are likely to continue into the future.”

Johnson said incorporating more data on births, deaths, and immigration into their analysis “resulted in a slower pace of population growth through 2060 than was previously projected” by the bureau. 

The bureau pointed out that “immigration is projected to become the largest contributor to population growth.”

“Reduced fertility and an aging population result in natural decrease — an excess of deaths relative to births — in all projection scenarios,” the bureau said.

Declines in fertility will further drive an increase in population age throughout the country, the press release said. The drop in fertility is “projected to shift the age structure of the population so that there will be more adults age 65 or older compared to children under age 18.”

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Immigration, the bureau said, could play a decisive role in ultimate population numbers. 

“Different levels of immigration between the present and 2100 could change the projection of the population in that year by as much as 209 million people,” the release said, “with the projected total population ranging anywhere from 226 to 435 million.”

The Census Bureau’s data on fertility rates reflect those recorded by the U.S. Centers for Disease Control and Prevention, which reported significant drops in fertility in many U.S. states over the years 2005–2021.

A 2019 study found a “new normal” of countries with fertility below the “replacement rate,” or the level of fertility at which a population replaces itself from one generation to the next.

In the Census Bureau release, Johnson suggested understanding demographic shifts such as these is critical for long-range planning at the societal level. 

“In an ever-changing world, understanding population dynamics is crucial for shaping policies and planning resources,” she said.