There are less than 11 million undocumented illegal aliens in the United States and it has been declining ever since for more than half a decade.

As of 2014, there are only around 10.9 million undocumented immigrants in the U.S. which is less than the previously recorded 12 million in 2008. The study by the former demographer of the U.S. Immigration and Naturalization, Robert Warren, also found out that there were more legally registered residents from Mexico that the undocumented ones between 1980 to 2014, according to the Journal on Migration and Human Security.

The undocumented population declined continuously from 2009 which is the time after the country's "Great Recession," which counters other claims that the population is increasing since the economy is getting back on track again, the study added.

"One reason for the high and sustained level of interest in undocumented immigration is the widespread belief that the trend in the undocumented population is ever upward," the report stated, according to Fox News Latino. "This paper shows that this belief is mistaken and that, in fact, the undocumented population has been decreasing for more than a half a decade."

However, as of the second quarter of 2015, there is a recorded number of 42.1 million immigrants in the United States, both legal and illegal. Immigrants comprise 13.3 percent of the U.S. population.

The number of immigrants has been increasing according to the recent study, but it must be noted that they are in the country legally; however, the Department of Homeland Security and other research bodies noted that an estimated eight immigrants out of 10 are from Mexico or Latin America which could be an indication that illegal immigration might be on the rise again in the future, according to the Center For Immigration Studies.