Shortly after then-candidate Donald Trump announced his presidential campaign, he suggested that the number of undocumented immigrants living in the United States could exceed 30 million. But a new study puts the number far lower and shows a significant decline over more than a decade.The study, published by the Pew Research Center on Tuesday, put the number of undocumented immigrants in the United States at 10.7 million in 2016, down from a peak of 12.2 million in 2007.As Pew analyzed new data from recent years, its researchers found that “it wasn’t just that the numbers declined, but also who these unauthorized immigrants are had changed since 2007,” said D’Vera Cohn, a senior writer at Pew Research.The estimates are derived from figures published by sources like the Census Bureau, which accounts for foreign-born people living in the United States, along with other demographic data including death rates and legal border admissions.The report showed that the immigration landscape was different from that portrayed by many politicians:In 2016, as President Barack Obama left office, the number of undocumented immigrants living in the United States was at its lowest level in a decade.As of 2016, the most recent data available, the number of people living in the United States without documents decreased to 10.7 million from a peak of 12.2 million in 2007. The sharp decline came largely during the Obama administration and in the wake of the Great Recession. Deportations also sharply rose during that time.“The recession and the housing bust were certainly important events driving down these numbers, but it’s also possible that several other things were important as well,” Ms. Cohn said. “We know that border enforcement was stepped up during this period too, and smuggling fees increased. And we also know there has been a rise in deportations.”Amid global economic and political shifts, there are fewer undocumented Mexican migrants today and more Central Americans. In 2016 there were 1.5 million fewer unauthorized Mexicans living in the United States than in 2007. While they still make up a majority of illegal immigrants living in the United States today, migration out of Mexico has slowed. Pew notes that, according to survey data by the Mexican government, “the majority cited family reunification as the main reason” for returning to Mexico.And there has also been a sharp decrease in the number of “recent arrivals” — immigrants who entered the country within the last five years. “There was an average of 386,000 annual unauthorized arrivals for the 2011-16 period, compared with 715,000 for the 2002-07 period. That amounts to a 46 percent decline,” according to the report. During that time, entering the country grew more difficult and, throughout the recession, jobs in construction and other fields grew more scarce.But in contrast, the number of migrants from Central America living in the United States illegally rose somewhat between 2007 and 2016, amid increased violence and economic uncertainty in the Northern Triangle region.The overwhelming majority of undocumented immigrants have lived in the country for a decade or longer.The typical undocumented migrant living in the United States in 2016 had been here for about 15 years, up from a median of about nine years in 2007. Two-thirds of all undocumented immigrants, the researchers found, had lived in the United States for more than 10 years.“This is a much more rooted, established population than it was in 2007,” Ms. Cohn said. “There are markedly fewer short-term residents and more long term residents.”One million immigrants without papers are protected from deportation by the Deferred Action for Childhood Arrivals program and other mechanisms.Pew estimates that about 700,000 people in the United States who were brought to the country without documents as children have received protection from deportation through DACA. An additional 300,000 have Temporary Protected Status, which is applied to migrants from countries like El Salvador and Haiti that have experienced natural disasters.Visa overstays have become an increasingly significant share of unauthorized migration.Because of limited statistical data, it is hard to account for how many undocumented immigrants in the United States are here as a result of overstaying a visa. But those migrants increasingly appear to make up a significant share of overall illegal immigration.“We don’t have exact numbers,” Ms. Cohn said, “but, from what we know, it appears that a majority of recent arrivals in 2016 are not unauthorized immigrants who crossed without documents, but people who arrived on legal visas and overstayed their deadlines to leave.”Such immigrants, who typically have the means to enter the country legally but have not been granted permission to stay beyond a certain period, “probably constituted most of the recent unauthorized immigrant arrivals in 2016,” according to the report.