The immigrant population in the United States hit a record high of 42.1 million in the second quarter of this year, an analysis of monthly Census Bureau data by the Center for Immigration Studies, released Thursday, has revealed. The number of immigrants rose by 1.7 million since the same time last year. Immigrants currently comprise 13.3 percent of the nation's total population, reaching the highest level in the nation in 105 years. 

"Illegal immigration came up in the presidential debates, but there has been little discussion of the level of immigration; this at a time when total immigration is surging according to the latest data," said Steven Camarota, co-author of the report and the center's director of research, in a statement.

Immigration has become a heated issue on the presidential campaign trail, with Republicans offering pointed criticism of the nation's acceptance of undocumented immigrants. While much of the discussion has surrounded immigrants from Mexico, migration to the United States from its southern neighbor dropped 17.7 percent from 2010 through 2013, data from the Department of Homeland Security show, as Forbes reported.

The number of immigrants arriving from Asia now roughly equals the number from other countries in North, South and Central America, Forbes reported. But the new study by Center for Immigration Studies suggests that the number of Latin American immigrants may be rebounding in the past year. 

"The rapid growth in the immigrant population was foreseeable given the cutbacks in enforcement, our expansive legal immigration system, and the improvement in the economy," Camarota claimed in the statement. 

Immigrant populations have increasingly moved beyond traditional high-density coastal cities like New York City and Los Angeles, with the highest immigrant population growth coming in heartland cities and the South. Pittsburgh ranks first for the pace of growth, with a 17.4 percent jump in its foreign population from 2010 to 2013, four times the national rate.