Yes, Illegal Immigration Can Be Controlled

By Steven A. Camarota

Thursday, July 24, 2025

 

For years we have heard that immigration is like the weather — it can’t be controlled, so get used to it. Open-borders advocate David Bier actually wrote a piece for the New York Times in 2023 titled “Biden Can’t Stop Immigration. Time to Embrace It.” In 2024, NPR assured us that, “despite a fortified border, migrants will keep coming.” While the scale of illegal immigration during the Biden administration was completely unprecedented, only a few months into the Trump administration, border encounters are down 93 percent. It turns out that illegal immigration can be greatly curtailed if the government is committed to actually enforcing the law.

 

But what about those illegal immigrants already here? A new analysis by me and my colleague Karen Zeigler shows that enforcement has significantly reduced the number of illegal immigrants in the country. We estimate that between January and May of this year, the illegal immigrant population declined by 1 million. Deportations have been only a small fraction of that number, so most of this decline must have been due to a big increase in emigration, almost certainly because of stepped-up enforcement.

 

How do we know this? Each month the government collects the Current Population Survey (CPS), which is the source of the unemployment rate and other labor market data. The survey also asks about place of birth, citizenship, and year of arrival. The Census Bureau, which collects the survey, and the Bureau of Labor Statistics, which analyzes it, are clear that it includes illegal immigrants, though the survey doesn’t account for all of them.

 

Before the recent decline, the CPS showed clear evidence of the border surge during the Biden administration. From January 2021, when Biden took office, to January 2025, when he left, the total foreign-born population, which includes legal and illegal immigrants, grew by 8.3 million. We estimate that two-thirds of the increase in the survey was from illegal immigration. The 53.3 million total foreign-born residents in January of this year is by far the highest number ever recorded in any government survey or census, as is their 15.8 percent of the total population. This surpasses the prior record percentage reached more than a century ago.

 

The 8.3 million-person growth in the foreign-born represents the net increase. The number of new arrivals is much larger than the growth but is offset each year by the roughly 750,000 foreign-born individuals who go home and roughly 300,000 who die. For the total number of the foreign-born to grow as much as it did during Biden’s term, at a minimum 12 million new legal and illegal immigrants had to arrive under his watch. Remember, the foreign-born population by definition can grow only from new arrivals; all children born here add to the native-born population.

Source: Public-use monthly Current Population Survey (CPS), January 2021 to May 2025. *Based on year-of-arrival question in the CPS.

One reason we know that illegals contributed greatly to the growth in the number of the foreign-born in the survey is that significantly more foreign-born people show up in the data every month than have been allowed into the country legally. In fact, most researchers, including those at the Department of Homeland Security, estimate the illegal immigrant population by subtracting the estimated number of legal immigrants in the country from the total immigrant population in government surveys. The leftover or “residual” provides a baseline number of illegal immigrants. There is more to it than that, but this is the basic approach.

 

Using that approach, we estimate that Biden started with 10.2 million illegal immigrants in January 2021. He left in January 2025 with 15.8 million. Our preliminary estimate using the May 2025 data finds that the illegal population has now fallen by 1 million, to 14.8 million.

Source: Center for Immigration Studies analysis of the public-use monthly Current Population Survey for January, February, and March, 2021 to 2024. Estimates in January and May of 2025 are based on only a single month of data.

The above numbers are adjusted for those missed by the survey. Most researchers, myself included, think the undercount of illegal immigrants in government surveys is not very large, so our estimates require only a modest upward adjustment of the number of illegal immigrants in the Current Population Survey. To see why, first consider, as noted above, that the survey captured an enormous increase in the overall foreign-born population that can only be the result of a huge increase in illegal immigrants in the data, since we did not let anywhere near that number of legal immigrants into the country.

 

In fact, we can see clear evidence of the rise in illegal immigration simply by looking at noncitizens from Latin America who said they arrived in 1980 or later. Prior research finds that about three-fourths of those in the United States illegally are from that region. As a result, the size of the noncitizen, post-1980 Latin American population is strongly correlated with the illegal immigrant population. The CPS shows that there was a huge increase in this population during Biden’s term. Since peaking in December, the month after Trump won, this population has fallen significantly.

 

The CPS clearly captures trends in illegal immigration. That said, many people still believe that the illegal population is much larger than the 14 million to 16 million the survey implies. There are a number of reasons why the 20 million or even 30 million figure for illegal immigrants sometimes cited is almost certainly wrong. First, comparing government surveys to administrative data, such as school enrollment and births, does not indicate that an enormous number of illegals are missing from government surveys. While it is possible that illegal immigrants have very low fertility or few children in public schools, it is extremely unlikely. If true, it would contradict everything we know about illegal immigrants, which is that they are relatively young and have a significant number of children.

 

Second, many people mistakenly think the number of illegal immigrants is much larger than it is because they confuse the unprecedented 11 million border encounters during the Biden administration with new additions to the illegal population. But encounters are often of the same person caught more than once. Further, millions of these individuals were released by DHS, but millions of others were sent back.

 

A third factor that leads many Americans to overestimate the illegal population is that the media seldom mention the enormous scale of legal immigration. In most years the U.S. gives out more than 1 million green cards (allowing permanent residency). In addition, several hundred thousand new foreign students, guest workers, and cultural-exchange visitors arrive annually and stay for multiple years. There are about 38 million legal immigrants in the country — one out of nine U.S. residents. Because many Americans do not realize this, they mistakenly assume that most of the immigrants they see around them must be here illegally.

 

The fourth and maybe the most important reason why so many folks overestimate the number of illegal immigrants is that they are unaware of all the people who exit the illegal population each year. Some die, about 60,000 annually, and a significant number, perhaps 300,000, leave each year. More important, our immigration system is so lax that over the past few decades, millions of illegal immigrants have been allowed to legalize by marrying an American, winning the visa lottery, becoming an asylee, and so on.

 

Robert Warren at the Migration Policy Institute, who has done the most detailed work in this area, estimates that in the time just between 2010 and 2019, 5.9 million illegal immigrants left the illegal population in various ways. So even though roughly 6 million new illegal immigrants entered in the decade before Covid, there was no net increase in the illegal population. Of course, during the Biden administration, the illegal population grew dramatically because the number allowed in was so large that it completely swamped the combination of deaths, emigration, and legalizations.

 

Furthermore, there are about 5 million U.S.-born children of illegal immigrants who were awarded American citizenship at birth and are therefore not counted in the illegal population. Adding these children to all the illegal immigrants legalized over the decades, plus the actual number of illegal immigrants, would put the total at something like 30 million. So, in a way, the public’s intuition is not entirely wrong. But the illegal immigrants themselves are only about half that number.

 

What happened during the Biden administration was totally unprecedented. At least 5 million illegal immigrants were released at the border or flown into the country. There were also more than 2 million “got-aways” at the border — those seen entering but not apprehended or turned back. In addition, some number joined the illegal population by crossing the border unseen or by overstaying a temporary visa. The public’s profound dissatisfaction with the massive increase in illegal immigration is understandable and one of the main reasons why Trump won in 2024. But any policy discussion on illegal immigration needs to be based on the best information available and not emotion and frustration, however understandable.

 

Of course, there is always uncertainty when estimating illegal immigration. It is possible that the undercount in the Current Population Survey is higher than most researchers think, so maybe the illegal population did peak at something like 17 million under Biden. But even if the survey missed a lot of illegals, it does not change the fact that it still shows a large decline in the illegal population since Trump took office. The biggest caveat about the recent drop-off is that it is possible that illegal immigrants are still here but that some are now too fearful to respond to the CPS. We do not think this is what happened, but it is a possibility.

 

The bottom line is that the best data available indicate that 1 million illegal immigrants have left the country since President Trump took office. It turns out that having a president committed to enforcing immigration laws appears to have caused a significant number of illegal immigrants to head home. Immigration is controllable. Voluntary emigration or “self-deportation” has played and can continue to play a huge role in reducing the illegal population if enforcement efforts are sustained.