That number of "unauthorized immigrants" represented 23 percent of the total U.S. foreign-born population of 45.6 million. Lawful immigrants comprised the vast majority with 35.2 million, or 77 percent. The remainder included lawful permanent residents (12.3 million) and temporary lawful residents (2.2 million), according to the analysis.
The report, posted Friday, came as presidential candidates offered ideas for tackling a growing immigration crisis.
Pew reached those numbers by estimating how many immigrants in the country were legal and subtracting that figure from the total number of migrants -- found through a census or national survey.
The number of illegal immigrants has become the subject of debate in recent years as differing estimates have emerged.
Many organizations have used Census data to estimate migration levels, but a joint study between Yale University and the Massachusetts Institute of Technology found much higher numbers through a different methodology.
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