Estimating Illegal Immigration at the U.S.-Mexico Border

Over the past decade, the U.S. Department of Homeland Security has stepped up its enforcement efforts at the U.S.-Mexico border while the number of unauthorized migrants apprehended at the border has decreased.  In order to determine whether DHS’s heightened enforcement contributed to this decline, it is critical to estimate the number of attempted border crossings during the same period.

Options for Estimating Illegal Entries at the U.S.-Mexico Border, a new report from the National Research Council, finds that making such an estimate will require combining DHS administrative data, survey data, and modeling approaches.  The report says that DHS should integrate apprehensions data from the U.S. Border Patrol, Office of Field Operations, and Immigrations and Customs Enforcement with existing survey data to produce useful insights about migrant flow and the effectiveness of border enforcement.  The agency should not invest in major changes to existing surveys or in implementing a new survey. 

In addition, DHS should sponsor and conduct research on modeling approaches for estimating immigration flows across the border.  These approaches and their underlying assumptions must keep track of the changing mechanisms of migration and be continually validated against historical trends and data.  To develop, apply, and refine modeling approaches, DHS will need to engage with the broader scientific community and make the data in its enforcement databases widely available to researchers.

The report is available for immediate release at  Media inquiries should be directed to the National Academies' Office of News and Public Information; tel. 202-334-2138 or e-mail