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Counting unauthorized immigrants: Easier said than done


“How many unauthorized immigrants are there in Virginia?” This is a question we get asked quite often, but there is really no good data or any official statistic on it. Migration numbers are difficult to estimate and counting the number of unauthorized or undocumented migrants can be especially challenging given the limited availability of records. Neither censuses nor surveys conducted by federal agencies directly ask the question of immigration status; they cover only citizenship. In the American Community Survey (ACS), which is the largest nationwide survey replacing the decennial census long form, individuals are asked about their citizenship status in the following three categories: native-born/U.S.-born citizen, naturalized U.S. citizen, or non-U.S. citizen. Non-citizens include both authorized and unauthorized immigrants, and there is no information about a non-citizen’s immigration status. In addition, since surveys require self-reporting, unauthorized immigrants tend not to answer the citizenship question or avoid filling out the survey altogether; therefore, some are missing even from the count of non-citizens. 

An individual’s nativity status refers to a person being native or foreign-born. The Census Bureau uses foreign-born to define those who are not U.S citizens at birth; which includes

  • naturalized citizens,
  • lawful permanent residents (immigrants with greencards),
  • temporary migrants (foreign individuals with students, business, employment or tourist visas),
  • humanitarian migrants (such as refugees), and
  • unauthorized migrants.

The Department of Homeland Security’s Office of Immigration Statistics (OIS) houses data on immigration status and releases factsheets and data visualizations, like this infographic below on main types of immigration covering foreign-born persons: lawful permanent residents (greencard holders), refugee arrivals, grants of asylum, naturalizations, and temporary admissions of nonimmigrants (students on F1, workers on H1B’s etc.).


In Virginia, 12.3% of the population is estimated to be foreign-born as per the 2016 ACS 1-year release, and this amounts to over a million people. Of these foreign-borns, more than half or 51% are naturalized citizens while the rest are non-citizens. Of the total number of foreign-born Virginians, 47% arrived before 2000, 32% entered the U.S. between 2000 and 2009, and the remaining 21% arrived between 2010 and now.

The estimates of unauthorized immigrants are calculated residually, meaning unauthorized immigrant population is the remainder or residual after the legally resident foreign-born population is subtracted from the total foreign-born population as described in the DHS report “Estimates of the Unauthorized Immigrant Population Residing in the United States” released in 2012. The DHS also provides estimates of the size of the unauthorized immigrant population residing in the United States by period of entry, region and country of origin, state of residence, age, and sex. The majority of the unauthorized resident immigrant population either entered the country without inspection or were admitted temporarily and overstayed the official date by which they were required to leave. As per their 2012 report, about 11.4 million unauthorized immigrants were living in the United States of which 78% (8.9 mil) were from North America (including Canada, Mexico, the Caribbean, and Central America); this was followed by Asia (1.3 million) and South America (0.7 million). The top 5 leading countries of origin for unauthorized immigrants are Mexico (6.7 million, representing 59 percent of the unauthorized population), El Salvador (690,000), Guatemala (560,000), Honduras (360,000), and Philippines (310,000).

There are some estimates about unauthorized immigrants at the national level released by the Pew Hispanic Center like their report on “Overall Number of U.S. Unauthorized Immigrants Holds Steady Since 2009”. These are based on indirect information and statistical simulation at the national level; estimates are available at the state-level but these are often less reliable.


Some small surveys, mainly designed for research purposes, ask immigrants to specify their immigration status. These surveys provide insights about some segments of unauthorized immigrants, but are not comprehensive and cannot be scaled up to estimate the overall unauthorized immigrant population. The following are a few examples of such surveys that include undocumented migrants:



  • The Los Angeles Family and Neighborhood Survey: L.A.FANS is a longitudinal study covering families in Los Angeles county and surrounding neighborhoods conducted by the RAND Corporation in collaboration with the UCLA School of Public Health.
  • The Mexican Migration Project: The MMP focuses on collecting socio-economic information on Mexican-US migration. It is a bi-national research endeavor overseen by faculty at the University of Guadalajara (Mexico) and at Princeton University (U.S.).
  • The National Agricultural Workers Survey: NAWS is an employment based random sample survey of migrant and seasonal crop workers in the U.S. and is administered by the Department of Labor.
  • Survey of Income and Program Participation: SIPP is a longitudinal survey run by the U.S. Census Bureau, with detailed monthly information from individuals aged 15 and older.

Because their identity is protected by anonymity, respondents are more likely to provide their information. In addition some of these surveys allow researchers to build a degree of trust and reciprocity over longer time periods.

In conclusion, there is no accurate count of the number of unauthorized immigrants. Even the data released on unauthorized immigrant populations at the national level are indirect estimates. Any estimates at the sub-national level should be used with extra caution.