CBO Paper: The Foreign-Born Population and Its Effects on the U.S. Economy and the Federal Budget--An Overview [open pdf - 349KB]
From the Document: "About 47 million people living in the United States in 2018 were born in other countries. Roughly three-quarters of those people were here legally. They included naturalized citizens, lawful permanent residents (who are also known as green-card holders), refugees, people who were granted asylum, and people who were temporarily admitted for a specific purpose, such as extended work or study. (The people accounted for in this document do not include visitors for business or pleasure.) The remaining one-quarter, or about 11 million people, were here illegally, having either remained here when their temporary legal status expired or crossed the border illegally. For more than a decade, the number of people remaining when their temporary status expired has exceeded the number crossing the border illegally, mostly because the number of illegal border crossings has declined."
Congressional Budget Office: http://www.cbo.gov/