When you think of illegal immigration in the U.S., do you picture a border crosser or a visa overstayer? A family or a single person? A farmworker or a waiter?

People living in the U.S. without legal status are frequently invoked in American politics —especially in recent months. But the conversation is often short on facts about the millions of people who fall into this category.

There are, however, outdated beliefs: A Pew Research Center survey in 2015 found that very few Americans are aware of recent changes in immigration patterns.

And, of course, there are stereotypes, which often don't always match up with reality. Most people in the U.S. illegally have been here for years, for instance, and people working service jobs far outnumber migrant farm labor.

Here's a look at the actual statistics about people living in the U.S. illegally.

We should note that there are a few caveats about this data. Different research groups use different methodologies, and in some cases, they rely on estimates. We've included links to all our data sources so you can read about their methods in more detail.

About 11 million people live in the U.S. without authorization

There are far more naturalized citizens than unauthorized immigrants in the U.S., and slightly more green card holders, according to the Pew Research Center.

The total number of people living in the country illegally — about 11 million — has made headlines recently, because immigration advocates suggest that under the Trump administration's immigration enforcement policies, almost all of them could be targeted for deportation. (More than 700,000 "DREAMers" — immigrants who were brought into the U.S. illegally or overstayed their visas as children — are still temporarily protected from deportation through the Deferred Action for Childhood Arrivals, or DACA, program.)

Longtime residents outnumber new arrivals

A large majority of those people currently living in the U.S. illegally have been here for a decade or longer, which is a major shift from the situation at the turn of the millennium.

About two-thirds of unauthorized immigrants have lived in the U.S. for 10 years or more, Pew says. Only 14 percent arrived within the past five years.

In the late 1990s, the number of new arrivals was far higher, and the share of longtime residents far lower.

Mexicans make up a dominant — but declining — share of this population

Mexico is "the leading nation of origin for U.S. unauthorized immigrants," Pew writes, but the share of immigrants from Mexico is also declining.

That is to say, Mexican immigrants are a shrinking majority of the population living in the country through illegal immigration.

Of people living in the U.S. illegally, more than half are from Mexico. The population from that one country far outnumbers the population from entire continents. But there are fewer people of Mexican origin living in the U.S. now than there were a decade ago.

You can see the trend lines clearly if you look just at people arrivingin the U.S. illegally, instead of the millions who live here. The percentage arriving from Mexico has dropped markedly, while more immigrants are coming from Africa, Central America and Asia.

The reasons for the shifting immigration patterns are complex. For Central American immigrants, conflicts in their home countries certainly play a role. The Migration Policy Institute suggests that there might be similar reasons for increased migration from Asia and Africa.

"As European countries have tightened migration restrictions after record inflows of asylum seekers and migrants in 2015, some Africans and Asians fleeing conflict and poverty appear to be flying to Latin American countries with relatively lenient visa policies, such as Ecuador, Brazil, and Cuba, then turning to established regional migration networks," the Migration Policy Institute writes.

Hundreds of thousands of unauthorized immigrants entered with valid visas

The Department of Homeland Security has estimated that as of Jan. 4, 2016, about 416,500 people overstayed their visas in fiscal year 2015. That's less than 1 percent of visa holders who entered the U.S. during that period.

Still, it's unclear how many visa overstayers make up the total number of unauthorized immigrants. A Pew estimate from 2006 says it could be as high as 45 percent. A recent study by the Center for Migration Studies estimates that two-thirds of those who joined the unauthorized immigrant population in 2014 were visa overstayers.

Why's it so hard to nail down the details? In part, it's because the data released last year are the first numbers on visa overstays that the government has released in more than two decades.

Federal law requires the Department of Homeland Security to report how many people come into the U.S. and stay after their visas expire. But the government has been having trouble collecting that data for years, as a study by the U.S. Government Accountability Office found.

The way airports and other ports of entry are currently set up makes it difficult to keep track of when a traveler leaves the U.S. The department has been piloting new programs to identify airport travelers by scanning their faces and irises.

Without historical data, it's hard to measure trends. But the estimates for fiscal year 2015 do show that Canadians made up the majority of visa overstays.

61 percent of unauthorized immigrants live in 20 metro areas — but most live in the suburbs, not the city

If you're a person living in the U.S. illegally, odds are you can be found in one of a few big cities and their surrounding suburbs.

Sixty-one percent of this population lives in 20 metropolitan areas, such as New York, Los Angeles and Houston, Pew reports. That's very different from the stats for the U.S. as a whole — just 36 percent of the overall population live in those areas.

But "metropolitan" doesn't mean "urban," and most people living there illegally reside in the suburbs instead of the city proper. (The only exception to that rule is Phoenix.)

That can pose a challenge for city governments that want to take a stand on immigration issues, as NPR's Richard Gonzalez reported last month:

"Many big city mayors have promised to resist President Trump's threat to cut off federal funds to sanctuary cities. But the fact that most of the unauthorized immigrants live outside of city limits might complicate a mayor's ability to protect them, according to William Frey, a demographer at the Brookings Institution.

"He told the Chicago Tribune, 'This may raise questions of whether or not the sanctuary status is an umbrella one that covers the whole region.' "

Most are working in service and construction jobs

You probably know that people living in the U.S. without legal status, as well as other immigrants, are a big part of the farm labor force.

That's why the farm industry and farmworkers have been keenly concerned about Trump's rhetoric and policies on immigration.

But there just aren't very many farming jobs in the U.S., overall. So farming is nota common industry for the 11 million — only 4 percent of people living here illegally work in agriculture.

Far, far more work in service jobs or in construction.

Many have children who are U.S. citizens

According to the Migration Policy Institute, one-third of people who are age 15 or older and staying in the U.S. without authorization live with at least one child under the age of 18 who is a U.S. citizen. That's far more than the number who live only with noncitizen children — that's just 6 percent of the population.

Jennifer Van Hook, a demographer at Penn State University who studies immigration, points out that this statistic shows that deportations affect more than just unauthorized immigrants.

"When these people leave the country, who's going to take care of their children? It's likely that some of those U.S.-born children will be accompanying their parents," she says.

Former President Barack Obama's attempt to temporarily shield these parents of U.S. citizens from deportation through Deferred Action for Parents of Americans and Lawful Permanent Residents — also known as DAPA — has never been implemented, and the future of the effort is unclear.

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