In the United States, elections are run by state governments. Each state is allotted a certain number of congressional representatives based on its population. The population of each state is determined by the census taken once every 10 years. The number of congressional representatives a state has both determines the number of representatives that state holds in the US House of Representatives and the number of electors allotted to each state in the Electoral College.

As an example, the State of New York had a population of 19,378,102 in the 2010 census. The Census Bureau allotted the State of New York 27 seats in the House of Representatives. With 2 seats in the Senate, the State of New York has 29 total electors in the 2020 Electoral College.

Now suppose that after the census was taken, a dramatic event happened that significantly and permanently shifted the population distribution among the States. I provide some examples below:

  1. A Nuclear Power plant explodes making a big city uninhabitable.
  2. Immigration law changes leading to a dramatic influx of new immigrants to coastal or border states like Washington, California, Texas, or New Mexico.
  3. A natural disaster like The Big One kills millions of residents.

If an event like one of these occurred, the true population of each state would no longer resemble the estimated population of each state from the Census. One might suspect that there would be calls to adjust population estimates in response to the disaster.

Has something like this happened before? Are there laws in place that would allow adjustments to population estimates in-between the 10-year censuses? If so, at what point of the election cycle would those adjustments be made?

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    A natural disaster need not kill millions of residents to have an effect on the census. If it just forces people to move to another district or even another state, that would have a similar effect. As an example, see the effects of Hurricane Maria on Puerto Rico, which caused many residents to move out of the territory, mostly to Florida and other nearby states, which will result in a sizeable change to their populations (and notably more people eligible to vote in a presidential election). Commented Oct 16, 2020 at 14:23
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    @DarrelHoffman I chose to have this hypothetical natural disaster kill millions of residents to emphasize that the population shift is permanent. If a hurricane only displaced millions of residents between now and the 2020 election, I don't think there would be a strong argument to adjust population estimates in affected states. If New York City disappeared in a giant sinkhole, I think it would be difficult to justify (politically... the OP is about the law and precedent) why the State of New York should continue to have 29 electors.
    – mana
    Commented Oct 16, 2020 at 14:46
  • The population has forgotten how to reproduce itself? Wow, that really would be a disaster. People move back after a disaster.
    – NomadMaker
    Commented Oct 16, 2020 at 15:03
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    @mana I mentioned this case only because it's significant that a large number of US citizens were displaced from a place where they can't vote for the President to one where they can (unlike immigrants from, say, Mexico, who would have to apply for and earn citizenship first). And a large percentage are likely to stick around rather than moving back, resulting in a lasting sizeable change to the demographics of both Puerto Rico and Florida (and possibly other places). Commented Oct 16, 2020 at 18:00
  • 4. A global pandemic causes people to move out of large cities... Commented Oct 17, 2020 at 1:53

2 Answers 2


The text of Article I states (with my emphasis):

... The actual Enumeration shall be made within three Years after the first Meeting of the Congress of the United States, and within every subsequent Term of ten Years, in such Manner as they shall by Law direct.

So, Congress may, by passing legislation, order a re-enumeration of the USA at any time. The manner of enumeration may be decided by Congress, so need not be a full census, (although any other method of enumeration would surely be challenged: as it must be an enumeration and not an estimate)

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    This is vastly complicated--and I think this is relevant to what OP's trying to ask about--by what the enumeration can be used for. Surely Congress can't just do a new enumeration every year or two and alter the apportionment of the House every election cycle, likely resulting in constant political gamesmanship (gerrymandering to the next level) to try to fudge the process to get what you want out of it. I believe in fact they do do fresh counts every couple of years for other purposes, but some of them are locked into the once per ten years cycle. Commented Oct 16, 2020 at 3:59
  • Anything outside of a full recount will be rightfully challenged in a court of law because the amount of representatives is based on a states population and the countries population as a whole. Which means you can't alter the number of representatives in a single state without having to change it in others.
    – Joe W
    Commented Oct 16, 2020 at 13:03
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    @zibadawatimmy it sounds like they could do this if they wanted to. I have to imagine that they don't because they don't expect the potential gains to be worth the trouble - it's unlikely to change any given state's voting power significantly, in the absence of a large scale population change.
    – James_pic
    Commented Oct 16, 2020 at 13:11
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    It sounds like there are already dramatic shifts of population away from states like New York, California, and Washington, just as the 2020 census is being taken. That means the census data could quickly become pretty outdated in this particular instance. Commented Oct 16, 2020 at 18:41
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    Note that current law allows the Census Bureau to conduct a mid-decade census "in such form and content as he may determine" (paragraph (d)), but that "[i]nformation obtained in any mid-decade census shall not be used for apportionment of Representatives in Congress among the several States, nor shall such information be used in prescribing congressional districts" (paragraph (e).) Commented Jan 13, 2022 at 19:50

Congress may pass laws to reappportion set the count of house seats and reapportion the states based on the Census when Congress cares to. Since 1929, there has been a "permanent apportionment" act so Congress has had no need to act to reapportion after subsequent Census enumerations.

If you're looking for historical examples of a dramatic change in voting population between states here's likely the biggest historical step change: enactment of the 14th Amendment. This removed the "3/5ths compromise" and increased former slave state enumerated population in an instant. The Apportionment Act of 1872 followed this step change.

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    It's not that they don't reapportion. They do, and have to. It's that they don't have to change the total number of seats. They've fixed it at 435, because they got tired of the time and politics spent on deciding how many seats to have (back then it was like the federal budget nonsense we have going on these days). Commented Oct 17, 2020 at 0:16

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