America's workforce is changing.

Baby Boomers are retiring and U.S. birth rates are falling. With fewer native born workers coming into the job market, the country is becoming more reliant on immigrants than ever before to keep its labor force growing, according to the Pew Research Center.

Today, immigrants make up about 17% of the U.S. labor force -- and nearly one-quarter of those immigrants are undocumented.

Without the current rate of both legal and undocumented immigration, Pew found that the total U.S. workforce would shrink dramatically over the next 20 years.

Related: Without immigrants, the U.S. workforce would shrink

Not only would that have an impact on overall economic growth, but it would hurt certain industries that rely heavily on immigrant labor, too.

After the housing market collapsed, the construction industry lost many of its foreign born workers -- many of whom moved back to Mexico and the Americas. Now, as construction ramps back up, home builders are having a difficult time staffing up.

Farmers are experiencing similar labor shortages, although many have said they've lost workers because of tougher enforcement of immigration laws that began during the Obama administration.

Back in the 1960's and 70's. The vast majority of immigrants to the U.S. came from Europe and Canada.

But that changed in the late 1990's and early 2000's, when millions of undocumented immigrants -- mainly from Mexico and the Americas -- crossed the border seeking higher paying jobs in the U.S.

Between 1995 and 2005, the number of undocumented immigrants in the U.S. workforce more than doubled from 3.6 million to 7.3 million, Pew reported. Most were Mexicans.

At the time, the Mexican economy was suffering while the U.S. was in the middle of a housing boom. Many Mexicans found construction jobs and other blue-collar work in the U.S. that paid substantially more than even white collar jobs in Mexico. As a result, Mexicans have represented the largest number of undocumented workers in the U.S. for the past 20 years.

Related: 1,500 economists to Trump: Immigrants are good for the economy

But things began to change during the Great Recession. Jobs, especially in hard hit fields like construction, became more scarce at the same time Mexico's economy started improving. Meanwhile, the Obama administration tightened security at the borders, keeping new arrivals from entering the country.

Today, there are 11 million undocumented immigrants living in the United States. About 8 million of those immigrants are working.

While the undocumented workforce grew rapidly for more than a decade starting in the mid '90s, things began to shift following the recession.

Related: More Mexicans seen leaving the U.S. than arriving

The number of undocumented immigrants in the workforce peaked at 8.3 million in 2009, but has since dropped slightly to 8 million.

Last year, Mexicans' share of the total undocumented immigrant population fell to 50%, reported Pew. It's the first time since 2005 that Mexicans didn't represent a majority of undocumented immigrants in the U.S.

While fewer immigrants are coming from Mexico, other countries are picking up the slack.

More new arrivals are coming from Asia than Mexico, for instance.

In 2015, there were 1.5 million immigrants from Asia. Asians represented 37% of the new arrivals that year, up from 22% in 2004, Pew reported. Meanwhile, new arrivals from Mexico declined to about 28% from 55% in 2004.

Pew projects that Asian immigrants will become the largest immigrant group in the U.S. by 2055.

New arrivals from Central America have remained steady and now represents a larger share. In 2015, about 1.8 million undocumented immigrants from Central America arrived in the U.S., or about 15% of the newly arrived immigrant population, Pew said.