About a month ago, DHS Secretary Kristi Noem held a press conference to announce that about “1.6 million illegal immigrants have left the United States population.” There was a lot of eye rolling among journalists, comparing Noem’s claim to Attorney General Pam Bondi’s claim that President Trump’s drug interdiction policies had saved 258 million lives, roughly 75% of the U.S. total population. However, in the weeks since Noem’s announcement, several data points have come in that suggest her estimate may be reasonably accurate; indeed, it might even be too low.

In August, the Pew Foundation released an estimate that the foreign-born population in the U.S. declined from 53.3 million at the beginning of the year to 51.9 million by the end of June—a decline of 1.4 million in just six months. The Pew report notes that the January count of 53.3 million was “the largest number ever recorded,” and that the decline this year will be the first decline in the immigrant population since the 1960s.

About the same time, the Center for Immigration Studies (“CIS”) estimated that the foreign-born population fell by 2.2 million in the first seven months of the year. CIS estimates that 1.6 million of those who left were in the country illegally. If its estimate is correct, it would indicate that about 600,000 immigrants left, despite having the option legally to stay.

The CIS report indicates that it relied in part on a report from the Bureau of Labor Statistics, which tracks the number of foreign-born workers. The BLS data show that the number of foreign-born workers peaked in March at 32.2 million, before falling to 30.8 million by August—a decline of 1.4 million. Even so, the level remains historically high, and numbers appeared to stabilize in late summer.

Last week, the Congressional Budget Office updated its demographic projections, based on changes in immigration patterns and enforcement since the beginning of the year.  It lowered its projection for the population in 2055 from 372 million to 367 million. The current population is about 350 million, so their projection suggests that the U.S. will only add 17 million new residents over the next 30 years. That will be the slowest population growth in the country’s history. It also projects that natural population growth (births minus deaths) will turn negative in 2031. At that point, any population growth will be entirely dependent on incoming immigrants. The CBO’s numbers still assume growth from immigration this year and in subsequent years. That certainly seems unlikely, at least for this year, given all the preliminary data showing that many immigrants have already left the country.

If the U.S. population declines this year, it will be only the second time in the country’s history. The only other time was in 2021, at the height of the COVID pandemic.

There will be those who decry a lower population trajectory as a calamity and those who celebrate it as a blessing. But the truth is that we are in uncharted territory. Classical economic theory holds that the change in economic activity is the sum of the changes in population and productivity, implying that a population decline will lead to economic contraction. However, many argue that there are conditions today that distort the classical theory. These include the negative impacts of a dysfunctional immigration system, declines in the proclivity of immigrants to assimilate, and a potential massive increase in productivity driven by technology, especially AI.

However, all these opinions about the advantages or disadvantages of slower population growth, or perhaps even a population that is declining, are nothing but speculation at this point. For 250 years, companies, institutions, governments, policymakers, and investors have been basing decisions on the assumption that our population will continue to grow each year. At a minimum, this new trajectory will require a major reset of those long-standing assumptions.

Author's note: We will be discussing the latest immigration numbers as well as the likely consequences of the new, more restrictive immigration policies at our Readers' Conference on November 8. If this is a topic you are interested in, you don't want to miss this discussion.