With immigration reform being a hot political topic in 2012 I am seeing a lot of reports that throw around numbers. The one I see cited most often is that there are 12 million illegal immigrants currently residing in the United States (as of 2012)

While these numbers do not seem unreasonably high, I am suspicious how reliable they could be. How would the government, or anyone, be able to accurately estimate the numbers for a population that is likely trying to hide their presence? Do they simply assume that the census counts are correct and that illegal immigrants are properly self-reporting their numbers to census takers? And if so, is there any evidence to support that kind of assumption?

  • 5
    @Eva "undocumented immigrants" is so stigmatizing - shouldn't we call them "documentation challenged immigrants"?
    – Golden Cuy
    Commented Mar 8, 2013 at 7:59
  • 6
    @Eva - no, the only stigmatization here is of people who entered this country legally by following rules and laws, by equating them to people who violated laws. Their distinguishing characteristic isn't that they lack documents, it's that they broke immigration law. If people want to avoid being stigmatized, they should avoid commiting crimes or misdemeanours, like the rest of us law abiding people do.
    – user5341
    Commented Mar 8, 2013 at 15:18
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    @Eva I'm not going to dispute your pointless edit but seriously. The first definition of alien is "n. A foreigner, esp. one who is not a naturalized citizen of the country where they are living". By definition an alien is a human being, regardless of any sci-fi hijacking of the term as an incorrect synonym for "extra-terrestrial".
    – KutuluMike
    Commented Mar 8, 2013 at 18:11
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    @Eval - DO try and at least learn the facts instead of going on 'feelings'. "Alien" is an official US government term for ANY immigrant (formal name for Green Card used to be "Alien Registration Card" or "Alien Registration Receipt Card (INS Form I-151)". Your "preferences" are severely insulting to those of us who went through the pain and hassle of following the lawful path to get to USA.
    – user5341
    Commented Mar 8, 2013 at 19:30
  • 2
    Except that immigrant does not mean the same thing. A naturalized citizen is still an immigrant but they are not an alien.
    – KutuluMike
    Commented Mar 9, 2013 at 17:08

1 Answer 1


Estimates of the Unauthorized Immigrant Population Residing in the United States: January 2011 Department of Homeland Security:

The unauthorized immigrant population is the remainder or “residual” after the legally resident foreign-born population -

  • legal permanent residents (LPRs),
  • naturalized citizens,
  • asylees,
  • refugees,
  • and nonimmigrants

- is subtracted from the total foreign-born population.

Data to estimate the legally resident population were obtained primarily from the Department of Homeland Security (DHS), whereas the American Community Survey (ACS) of the U.S. Census Bureau was the source for estimates of the total foreign-born population.


In summary, an estimated 11.5 million unauthorized immigrants were living in the United States in January 2011 compared to a revised 2010 estimate of 11.6 million.



In general, caution is recommended in interpreting changes in the size of the unauthorized population presented in this report.

Annual estimates of the unauthorized immigrant population are subject to sampling error in the ACS and considerable nonsampling error because of uncertainty in some of the assumptions required for estimation (see Limitations below).



Two populations are estimated in order to derive the unauthorized population estimates:

  • 1) the total foreign-born population living in the United States on January 1, 2011 and
  • 2) the legally resident population on the same date.

The unauthorized population is equal to 1) minus 2).



  • Assumptions about undercount of the foreign-born population in the ACS and rates of emigration

  • Accuracy of year of entry reporting

  • Assumptions about the nonimmigrant population estimate

  • Sampling error in the ACS

  • Accuracy of state of residence for the non-naturalized legally resident population



Age - Sex


  • An estimated 11.5 million unauthorized immigrants were living in the United States in January 2011
  • The DHS report does discuss limitations/errors in estimates

For more detailed information about the estimates and their limitations click the link above.


  • What's not clear here is how do they estimate the "total foreign-born population"?
    – vartec
    Commented Sep 10, 2012 at 15:25
  • @vartec - The linked report has some details on how the number was estimated.
    – Oliver_C
    Commented Sep 11, 2012 at 15:36
  • Are there reliable estimates confirming DHS numbers from sources that don't have political reasons to downplay the number? I have definitely seen 20 Mil estimates floating around, but not sure how reliable they were.
    – user5341
    Commented Mar 8, 2013 at 15:24
  • The gender by age chart is interesting. There has to be reasons for deviations from the 1::1 ratio. Presumably the younger ages are close because they're part of family units that would have been brought to the country regardless of sex. The high descrepancy between 18-24 indicates that the great majority of illegal immigrants of that age are male. I wonder if the ratio evening out at an older age is because there are more illegal 'older' women entering the country, or is it a function of aging and an unequal death rate? Commented Mar 8, 2013 at 18:46
  • @user5341 - what would be the reason for non-political analysts at the DHS to cook the numbers? Commented Sep 13, 2016 at 16:27

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