Almost one-fifth of United States residents are either immigrants or American-born children of immigrants, according to a study released by the Center for Immigration Studies.

The right-leaning organization collected U.S. Census data from December 2015 to estimate 61 million immigrants, either legal or undocumented, currently live in the country. Of those 61 million, three-fourths, or 45.3 million, are here legally. The other 15.7 million are presumed undocumented, though the study doesn't identify specific nationalities.

"These numbers raise profound questions that are seldom asked," wrote Steven A. Camarota, CIS director of research. "What is the absorption capacity of our nation's schools, health care system, infrastructure, and, perhaps most importantly, its labor market?"

Researchers defined foreign-born immigrants as legal permanent residents, guest workers, undocumented residents and those who gained citizenship after arriving. They called the influx of immigrants arriving over the last 45 years "nothing short of astonishing," noting that the number of adults and children age 18 or younger entering the U.S. has risen by 18.4 million since 2000.

The population also developed faster in some states than others.

Since 1970, immigrants living in North Carolina ballooned from 47,000 to 1.43 million. In Georgia, the number grew to 1.75 million at a rate 25 times faster than the state's overall population. Rates in Arizona, Oklahoma, Texas and Virginia went up about 1,000 percent in the same period. Nevada, which recently hosted Democratic and Republican caucuses and maintains one of the country's largest Latino communities, has seen its immigrant population grow to 821,000, according to the Center's analysis.

"With some 45 legal immigrants and their young children already here, should we continue to admit a million new legal permanent immigrants every year?" Camarota wrote.

Declining Trends

While CIS researches cite studies from institutions like the Pew Research Center in their estimate of 15.7 million undocumented immigrants, they don't give much weight to how drastic the decline of incoming immigrants has been over the last decade.

The number of undocumented immigrants entering the U.S. has slowed every year since 2008, according to a Center for Migration Studies report released in January. The CIS uses this study to note that 10.9 million people have crossed the border since 2014, but doesn't mention that this is the lowest rate since 2003.

Last December, the Department of Homeland Security released its end of Fiscal Year 2015 statistics and said, among other things, that apprehensions along the southwest U.S.-Mexico border are at their lowest level in 40 years.

"Last year's removal numbers reflect this Department's increased focus on prioritizing convicted criminals and threats to public safety, border security and national security," said Homeland Security Secretary Jeh Johnson. "The removal numbers were driven by the dramatic decrease in those apprehended at the border in FY 2015 - 337,117 - the second lowest apprehension number since 1972, reflecting a lower level of attempted illegal migration at our borders."

Immigration Reform in an Election Year

The Obama administration began 2016 with a series of raids aimed at deporting undocumented women and children who arrived from Central America over the last two years. After receiving harsh criticism from Latino advocacy groups, Obama backtracked and clarified that ICE would only target convicted criminals going forward.

The raids began during the 2016 presidential election season, a time marred by negative portrayals of immigrants entering the country, primarily from GOP candidates. Republican front-runner Donald Trump and Texas Sen. Ted Cruz have each vowed to build a fortified wall along the border, something Trump claims he would force the Mexican government to pay for.

Next week, conservative Floridians will cast their votes for their ideal Republican presidential nominee. The Sunshine State is home to the country's third-largest Latino population, mostly made up of Cubans and Puerto Ricans.