Key facts about the changing U.S. unauthorized immigrant population

Border Patrol apprehensions of migrants at the U.S.-Mexico border are on the rise again. Although the majority of people attempting to enter the United States illegally are stopped, this trend could foreshadow an increase in the U.S. unauthorized immigrant population after years of relative stability. Yet the activity at the southwestern U.S. border is only one part of the overall story of unauthorized immigration, as a growing share of this population came from regions other than Mexico or Central America and entered the U.S. legally but overstayed their visas.

The unauthorized immigrant population is always changing and churning. The total number in the country can remain stable or decline even as new immigrants enter illegally or overstay a visa, because some voluntarily leave the country, are deported, die or become lawful residents. In short, the dynamic nature and pace of migration patterns has resulted in an unauthorized immigrant population whose size and composition has ebbed and flowed significantly over the past 30 years.

Here are key facts about this population and its dynamics.