The number of undocumented immigrants in the United States fell to 10.7 million in 2016, its lowest level in a decade, according to a new study by the Pew Research Center.

That drop occurred before Donald Trump became president and undertook extensive, ongoing efforts to tighten immigration rules and enforcement. It lends strength to the argument that former President Barack Obama was tougher on immigration than most people realized at the time.

Pew senior writer and editor D'Vera Cohn said tougher border enforcement and the U.S. economy likely contributed to the drop. The recession and housing-market downturn shrank the job market, and recovery has been slow. At the same time, stricter enforcement could discourage some migrants from coming here, and deportations also had an impact, she said.

The drop in undocumented immigrants, from a peak of 12.2 million in 2007, stems from a sharp decrease in the number of Mexican people entering the United States without papers, the study said.

While the number of unauthorized Mexican immigrants declined by 1.5 million from 2007 to 2016, that nation's border remained a pathway for growing numbers of people from El Salvador, Guatemala, and Honduras. Total undocumented Central American immigrants increased by 375,000 during the same time.

Mexicans still constitute about half of all undocumented people in the U.S., the study said.

In Pennsylvania, the number of undocumented immigrants dropped from a peak of 190,000 in 2014 to 170,000 in 2016. In New Jersey, the top of 550,000 occurred in 2007, and was down to 475,000 in 2016.

Pew based its estimates on 2016 government data and its own decade-plus worth of research on international migration. Data for 2017 was not immediately available.

The shrinking overall number of undocumented immigrants, the study said, comes from a very large drop in new immigrants entering the county. Today's population includes a smaller share of recent arrivals, especially from Mexico. It's also likely that a rising share of undocumented people entered the country with legal visas, then overstayed their scheduled departure.

The study also found:

  • Undocumented immigrants are less likely to be short-term residents. The share who have lived in the U.S. for five years or less was 18 percent in 2016, down from 30 percent in 2007.
  • Most children living with undocumented parents were born in the U.S.
  • While the overall American labor force has grown since 2007, the number of undocumented workers declined. In 2016 an estimated 7.8 million migrants ages 18 and older were in the workforce, the first time since 2006 that the number declined much below 8 million.