President-elect Trump has promised to deport millions of people who are living in the United States without permission. This population is commonly referred to as “undocumented,” “unauthorized” or “illegal.” But these terms are not entirely accurate. A significant number are in the country with temporary permissions — though many are set to expire during Mr. Trump’s term.

For the last decade, the best estimates put this population at around 11 million. But the number of people crossing U.S. borders reached a record level in 2022 before falling last year. More recent estimates put the number of people without legal status or with temporary protection from deportation at almost 14 million in 2024.

Many of them have permission to be here, at least for now.

“It’s true that immigration is high, but it’s hard to sort out who is an undocumented immigrant,” said Robert Warren, a demographer and the former statistics director at what was then the U.S. Immigration and Naturalization Service. “Most of the public looks at everyone as undocumented — asylum-seekers, T.P.S., DACA — but it’s important to really figure out who is included.”

The New York Times compared estimates from several research organizations and the federal government, as well as more recent administrative data, to better understand who these immigrants are, how they got here, and which of them may be most vulnerable to deportation under Mr. Trump.

Those with permission fall under the protection of many different programs.

What is perhaps most surprising — or misleading — about terms like “undocumented” and “unauthorized” is that as many as 40 percent of the people in this group do have some current authorization to live or work legally in the United States, according to one estimate by FWD.us, an immigration advocacy group that hired a demographer to study the population.

In an effort to deter illegal crossings, the Biden administration created a way for migrants to make an appointment to cross the southern border through a smartphone app called CBP One. The administration also created special pathways for people fleeing humanitarian crises in Afghanistan, Cuba, Haiti, Nicaragua, Ukraine and Venezuela and extended temporary protection from deportation for people from certain countries through a program known as Temporary Protected Status.

Immigrants who enter the country through these programs are following the current rules, but Mr. Trump and other Republicans have attacked them and said the programs are illegal.

Millions more people have applied for asylum and are allowed to remain in the country while their cases wend through immigration court — though very few asylum claims are ultimately granted. An Obama-era program known as DACA protects from deportation about 540,000 undocumented people brought to the country as children.

The Biden administration also deferred deportation for other groups of people, like those who have applied for protection because they were victims of or witnesses to a crime.

Trump has limited power to immediately remove these groups.

Many of the permissions offering humanitarian relief are set to expire during the Trump administration, including some that Mr. Biden recently extended. If the incoming administration were to try to end these protections sooner, it would likely face lawsuits.

Mr. Trump could immediately stop accepting new applications for humanitarian parole. It may be harder to cancel the status of those who are already here.

Nor can Mr. Trump easily deport the 2.6 million people who are awaiting a hearing or a decision on an asylum claim. He could try to hire more immigration judges to decide these cases, but even with a significant infusion of new funds, it would take years to work through the backlog.

DACA is no longer accepting new applications, and the future of the program is uncertain because of a lawsuit filed by several Republican state attorneys general.

People can have more than one status, and many of these groups overlap.

Many people in the country with temporary permission fall under overlapping programs.

For example, the bulk of the people who arrived through one of the Biden-era humanitarian pathways were granted parole for two years. Many of them now also have Temporary Protected Status. Along with those who used the CBP One app to cross the southern border, they can also apply for asylum within the first year they are in the United States.

These immigrants come from all over the world.

More than half of those who are in the United States without authorization have been here for 10 years or more.

Mexicans remain by far the largest group of people living in the country without authorization, but their share has declined significantly since the 1990s, according to data from the Pew Research Center.

An influx of people fleeing humanitarian and economic crises came from Central America during Mr. Trump’s first term, and many of them are still in the country.

Mexican officials and other leaders in the region say they have not been able to meet with the incoming administration about its deportation plans.

Few immigrants can be swiftly removed. Even fewer are in custody.

Out of all those who are unauthorized, Mr. Trump has said the top priority for deportation will be criminals. There are around 655,000 noncitizens living in the U.S. with criminal convictions or pending charges, according to data from Immigration and Customs Enforcement, though many of these charges are for minor offenses such as traffic violations.

There were about 39,000 immigrants in ICE custody at the end of December, near capacity for holding facilities.

The Trump administration may also focus its enforcement efforts on the nearly 1.4 million people whom an immigration judge has already ordered to be removed from the country.

Many of the rest have been living in the country for years and have developed ties to their communities, including having children born in the United States. It would require a significant amount of time and resources to locate and remove them.