Fact check: How are illegal alliens actuall ycounted in the usa

1. Summary of the results

The counting of unauthorized immigrants in the United States relies on sophisticated statistical methodologies rather than direct enumeration, as this population cannot be counted through traditional census methods. Two primary research organizations use different approaches to estimate this population:

Pew Research Center employs a residual estimation methodology that compares demographic estimates of lawful immigrants with the total immigrant population measured by the American Community Survey (ACS) or the March Supplement to the Current Population Survey ^[1]. Their estimates are adjusted for survey omissions and other errors, with the ACS providing more accurate results due to its larger sample size compared to the Current Population Survey ^[2]. Pew estimated 11.0 million unauthorized immigrants in the US as of 2022, with 3 million having temporary protection from deportation ^[3].

The Migration Policy Institute (MPI) uses a three-stage method involving data from the American Community Survey, the Survey of Income and Program Participation, and federal agency administrative data ^[4]. Their process identifies noncitizens likely to have legal status and uses statistical modeling to assign immigration status based on respondent characteristics ^[4].

The Federation for American Immigration Reform (FAIR) provides significantly higher estimates, claiming 18.6 million illegal aliens reside in the United States as of March 2025, accounting for undercounting challenges ^{[5] [6]}.

2. Missing context/alternative viewpoints

The original question lacks crucial context about the inherent challenges and limitations in counting unauthorized populations. The analyses reveal several important factors:

• Undercounting is a persistent problem, particularly among recent arrivals who may be reluctant to participate in surveys ^[7]
• Visa overstays constitute a significant portion of the unauthorized population, with an estimated 854,000 nonimmigrant visitors violating visa terms in Fiscal Year 2022 ^[6]
• Geographic and demographic shifts are occurring, with fewer unauthorized immigrants from Mexico and more from countries like El Salvador, India, and Guatemala, while the population becomes less geographically concentrated ^[3]

Different organizations benefit from promoting different estimates:

• Research institutions like Pew Research Center and MPI benefit from maintaining credibility through conservative, methodologically rigorous estimates
• Immigration advocacy organizations like FAIR may benefit from higher estimates that support arguments for stricter immigration enforcement and highlight fiscal costs, claiming illegal immigration costs US taxpayers approximately $182.1 billion annually ^[6]

3. Potential misinformation/bias in the original statement

The original question uses the term "illegal alliens" (with spelling errors), which reflects politically charged language. The analyses show that research organizations typically use more neutral terminology like "unauthorized immigrants" or "unauthorized aliens."

The question implies there might be a straightforward counting method, when the reality is that no direct counting occurs. Instead, researchers rely on complex statistical modeling and residual estimation methods using multiple data sources including the US Census Bureau's American Community Survey, Current Population Survey, and Department of Homeland Security administrative data ^[1].

The wide variation in estimates - from Pew's 11.0 million to FAIR's 18.6 million - demonstrates how methodological choices and organizational perspectives can significantly impact results. This variation suggests potential users of these statistics should carefully consider the source's methodology and potential institutional biases when interpreting the data.