Given how easy it is to register to vote in the US as a non-US citizen, it seems plausible that a non-zero number of such persons are on the electoral rolls in the US. There are statistics which show a very low number of reported voter fraud cases, but at the same time such statistics are useless unless the voting officials are focused on catching immigrants voting illegally. This therefore raises the following question...

Did any US state ever conduct a wide scale attempt to verify what percentage of voters on its electoral rolls are actually US citizens? I know that there isn't a comprehensive database of every US citizen available anywhere, but at the same time it should be possible to verify if a given voter is an American citizen given enough effort.

  • Comments deleted. This is not the place to discuss the advantages or disadvantages of voter ID laws. Please only post comments which help to improve the question.
    – Philipp
    Mar 28, 2018 at 16:40
  • This would be an impossible task as they don't collect enough information during registration in the first place. They would have to visit every voter and collect a birth certificate or full SSN number then verify them to ascertain citizenship.
    – Chloe
    Mar 28, 2018 at 23:57
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    There are good statistics on the percentage of people who are foreign born adults at the fine grained level of census tract data, which doesn't exactly track citizenship but is a good upper bound, and there are good statistics on the number of foreign born people naturalized in each state, each year. So a maximal percentage with 100% fraud is easy to quantify, and you can use other data to estimate what percentage of non-citizens are voting on average and multiply the two to get a fairly decent, highly localized estimate. This % is particularly low in places where there is the most concern.
    – ohwilleke
    Mar 30, 2018 at 6:17
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    @Chloe the social security number has very little bearing on one's citizenship. Anyone who has ever been authorized to work in the US has one, including hundreds of thousands of noncitizens, many of whom are no longer even authorized to live or work in the US.
    – phoog
    Mar 30, 2018 at 11:57

2 Answers 2


See Nation Council of State Legislatures, almost all states take efforts to purge voter registration rolls of ineligible persons, including those persons who are ineligible because of citizenship. The reason for NOT expending effort tp "conduct a wide scale attempt" by targeting the subset of non-citizens is that it has been determined time and again that the number of non-citizens that attempt to vote is exceedingly low (but admittedly greater than zero). BTW, voting officials are always on the lookout for people attempting to vote illegally, not just non-citizens.

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    Presumably "not non-zero" isn't what you meant to say there, because at the moment you are claiming the number is exactly zero, and that's easily disproven.
    – Ben Voigt
    Mar 29, 2018 at 6:13

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There is good information on the foreign born population of every county in the United States (and for that matter, every census tract), which is broken down by age as well.

There is good information on the number of persons naturalized in each state going back more or less indefinitely, which when compared to the number of foreign born people in each state can be used to determine the percentage of foreign born adults in each state who are not U.S. citizens, and extrapolated to the county level foreign born statistics to get a good approximation of the number of adult non-citizens in each county in the U.S. Just under half of foreign born persons are naturalized U.S. citizens. About 7% of the U.S. population consists of foreign born non-citizens, while 6% of the U.S. population consists of naturalized citizens of the United States.

As the map indicates, for the vast majority of counties in the United States, the foreign born population is very low. Only one in twenty of non-citizens in the U.S. live outside major metropolitan areas, while one in six native born citizens do.

And, one can use survey data and more isolated efforts to determine these figures to estimate a credible percentage of non-citizens who are registered to vote or do vote.

"As of 2015, the five counties with the largest foreign-born populations (Los Angeles County, Calif.; Miami-Dade County, Fla.; Cook County, Ill.; Harris County, Texas and Queens County, N.Y) account for 19% of the national immigrant population in the U.S." Source (citizen and non-citizen alike). Outside greater DC, greater NYC, Detroit, Florida, Texas, Nevada and the Pacific States, and a few other states in the Southwest, the maximum number of non-citizen voters even if an absurdly high (relative to reality) 5% adult non-citizens were voters, is negligible.

Also, since most of the concern about non-citizen voters is ultimately driven by the concern of conservatives that non-citizen voters will flip elections for Democrats, it is worth noting that most counties with lots of non-citizen adults are also overwhelmingly Democratic by margins that far exceed the highest imaginable percentage of non-citizen voters in any reality based analysis, and another significant percentage of those counties are very safe Republican leaning counties, where again, non-citizen voters wouldn't make a difference in outcomes.

The number of counties where non-citizen voting could conceivably make a difference so as to justify a comprehensive study of the type suggested in the original post, is very small, and predominantly limited to Florida. So, part of the reason that such studies are rare is because the justification for them is so weak.

  • Same conclusion "justification is so weak". Not filtered out of the foreign-born population ( and potentially illegal voters) are US citizens born to US citizen parents as well as registrants born in Puerto Rico, Guam etc. Good answer
    – BobE
    Mar 30, 2018 at 14:08
  • Wouldn't the number be sufficient to change the outcome on federal elections though? E.g. Florida is a swing state so you don't need that many votes to elect a different president. Mar 30, 2018 at 16:03
  • @JonathanReez To be clear, I specifically said that significant non-citizen voting could plausibly impact election outcomes in Florida if it took place at a high rate in the very last paragraph, even though it is very unlikely to have an impact anywhere else. So, if there was justification at all for doing a comprehensive study, that would be where it would make the most sense. (Florida is also unique in that it has a large foreign born sub-population, Cubans, who have historically leaned right politically, so its foreign born population is less partisan overall.)
    – ohwilleke
    Mar 30, 2018 at 17:13
  • I presume California could also be affected in Congress elections, especially during the off-cycle when turn out is low. They could also have affected the introduction of "sanctuary city" laws by voting in places like San Francisco. Mar 30, 2018 at 17:31
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    Focusing on Florida: To flip the vote in the last four presidential elections would have required, respectively one voter out of: 161 (2016), 227 (2012), 70 (2008), 39 (2004). So not only have elections been close, but the number of EC makes Florida very significant. Now the Florida legislature controls the registration and voting processes. That legislature has been Republican dominated for the last twenty years, so Florida would been the most likely to conduct the study you have asked about. And yet the FL legislature has not acted.
    – BobE
    Mar 30, 2018 at 18:37

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