Sen. Marco Rubio, R-Fla., a possible vice presidential pick for former President Donald Trump, said he supports Trump’s promise to carry out the largest deportation operation in the country’s history.

“If reelected, Donald Trump has said he’s willing to build migrant detention camps and deploy the U.S. military to deport the more than 11 million undocumented immigrants in this country,” NBC News host Kristen Welker said in a May 19 interview. “It would be the largest deportation operation in American history. Do you support that plan?”

Before saying that he would support the plan, Rubio rebutted Welker’s assertion that there are 11 million people living in the U.S. illegally.

“Eleven million? That’s an outdated — that was the number 10 years ago,” Rubio said. “We’re talking upwards of 20, 25, maybe 30 million. There’s been almost 10 million people that have entered this country in the last three years.”

Is Rubio right that the population of people living in the U.S. illegally doubled and has reached 20 million to 30 million?

Immigration groups’ estimates don’t support Rubio’s statement.

“The several organizations that have long issued authoritative data based on rigorous methodologies estimate that the unauthorized population is more in the 11 million range,” said Michelle Mittelstadt, communications director for the Migration Policy Institute, a nonpartisan think tank.

Rubio’s office did not answer our request for comment. Here’s a look at how groups estimate the number, and why Rubio’s calculation is wrong.

Estimating the population of immigrants living in the US illegally

In April, the Department of Homeland Security estimated that as of January 2022, 11 million unauthorized immigrants were living in the U.S. That’s up from the 10.5 million estimated in January 2020.

DHS and immigration groups usually publish these estimates annually. Every group has its own methodology, but collectively, the groups rely on data from the Census Bureau, some specifically use its annual American Community Survey, which documents changes in population, workforce and housing.

The groups calculate their figures by subtracting the number of immigrants legally in the country from the total number of foreign-born people. Then the groups estimate how many people are undercounted. That final number is their estimate of people illegally in the country.

After remaining largely unchanged for more than a decade, the number of immigrants in the U.S. illegally has risen under President Joe Biden’s administration. But not by as much as Rubio says.

“The methodology and data being used by demographers today provides strong statistical evidence that the undocumented population residing in the United States in January 2022 was about 11 (million) to 12 million,” said Robert Warren, a demographer and senior visiting fellow at the Center for Migration Studies of New York, a think tank studying international migration.

Here are immigration groups’ recent estimates of the number of people illegally in the U.S. They issued their estimates from November 2023 to March 2024:

• 11.2 million in 2021, up from 11 million in 2019, the nonpartisan Migration Policy Institute.
• 10.5 million in 2021, up from 10.2 million in 2019,  the nonpartisan Pew Research Center.
• 10.9 million in 2022, up from 10.3 million in 2021, the Center for Migration Studies of New York.
• 12.3 million in May 2023, up from 10.2 million in January 2021, the Center for Immigration Studies, a think tank favoring low immigration levels. Steven Camarota, the center’s research director, recently provided PolitiFact with a preliminary estimate of 14 million people in the country illegally as of March 2024.
• 16.8 million in 2023, the Federation for American Immigration Reform, a group advocating for reduced immigration.

Why immigration encounters alone can’t predict the unauthorized immigrant population

Under Biden’s administration, immigration officials have encountered immigrants trying to illegally cross the border more than 9.5 million times.

But that doesn’t mean that nearly 10 million more people are now living in the U.S. illegally.

Encounters represent events, not people. If one person tries to enter the country three different times and is stopped each time by border officials, for example, that equals three encounters, even if it’s the same person encountered.

“It’s too simple to suggest based on record arrivals at the U.S.-Mexico border that the unauthorized population is swelling by many millions of people,” Mittelstadt said.

Also, not everyone encountered illegally crossing the border is allowed to settle in the U.S. As of January 2024, the latest month with available data under Biden, around 3.9 million encounters had resulted in people being removed, returned or expelled from the U.S.

Besides encounters, DHS estimates that about 391,000 people have evaded border authorities. (The latest “got-aways” data DHS has published is for fiscal year 2021, which ran from Oct. 1, 2020, to Sept. 30, 2021, and includes about four months of the Trump administration.)

Also, the number of people living in the U.S. illegally isn’t affected just by people entering the U.S. The figure isn’t static, the Migration Policy Institute said in a March analysis. People die, leave the U.S. or change immigration status.

Our ruling

Rubio said the number of people in the U.S. illegally is “upwards of 20, 25, maybe 30 million.”

The number of immigrants living illegally in the U.S. has increased under Biden’s administration after remaining stable for years. But it is not as high as Rubio says. Most immigration groups that estimate this population agree the number ranges around 11 million to 12 million people, despite differences in methodologies. The highest estimate is 16.8 million.

Immigration officials don’t let in everyone they encounter, agents have expelled migrants millions of times under Biden. And the number of people living illegally in the U.S. is not static; it fluctuates as people die, leave the U.S. or change their immigration status. Adding the number of border stops under Biden to the estimated number of people already here illegally won’t produce an accurate total.

We rate Rubio’s statement False.

This fact check was originally published by PolitiFact, which is part of the Poynter Institute. See the sources for this fact check here.