After every US election, in seemingly every state, there are a handful of precincts that are very slow to report. Sometimes they are several hours or even days behind the majority of precincts in their area. I understand that states that span multiple time zones can be an issue, but to me it seems like there is no excuse to not have all election results in by late that night, or at least the following morning. What causes this delay?
The answer will vary by jurisdiction. The State of Washington for example, uses a vote-by-mail system with a requirement that ballots be received or postmarked by election day. Certification of election results may take up to 21 days for a general election, under the relevant state code. Ballot processing is subject to strict controls to prevent double-voting and maintain confidentiality, yet is open to observers.
In other states, other issues have surfaced, including the now famous hanging chad problem in Florida. This serves to illustrate how close races may be unwise to call early.
Virginia election in November 2017: headlines read A single vote on a puzzling ballot has control of Virginia's legislature hanging in the balance and the story shows the actual ballot in question.
The photos of Dewy Beats Truman headlines also come to mind, though admittedly dated (and before my time.)
The voting system is staffed by humans. Some will have been doing this every two years for decades, others are new at it. Some are "fussy" and slow, some are "confident" and quick.
Voter turnout is traditionally rather low. That means turnout in a few districts could conceivably double if there was some controversial/important proposal or race on the ballot that affects people there.
Unless one polling station is slow year after year, you might be looking at the effects of the statistical distribution. Someone has to be first, someone has to be last, and with so many polling stations there will be quite a difference between the first and last.
That can easily explain a couple hours difference on election night.
After every US election, in seemingly every state, there are a handful of precincts that are very slow to report. . . . What causes this delay?
There are 10s of thousands, if not 100s of thousand of precincts in the United States. Some will be faster and some will be slower. Some handful of those precincts will necessarily be the slowest. They will be, by definition, in the 99.9th to 99.99th percentile for slowness.
Basically, imagine that everything that could possibly go wrong does go wrong in some precinct.
For example, maybe the chief election administrator in the precinct gets sick midway through the process and leaves without explanation or filling out the proper paperwork, and the power goes out, and the ink used to mark ballots with was unusually smudgy, and the people charged with reading the ballots are in their 80s and almost legally blind, and the truck bringing the ballots from one of the voting locations to one of the counting locations gets a flat tire, and someone spills coffee on the tally being kept when they are almost done and they have to start over, and there is a dispute over the procedures for counting that results in a three hour argument before it is resolved but nobody bothered to read the instructions so they have to reread them on the spot, and the law requires that four people be on hand to count every ballot but one of the four people refuses to keep working after 10 p.m. because their babysitter can't stay after that hour even though ballot counting in a high turnout year isn't finished, etc.
Also, some local governments deliberately underfund election administration because it is only a problem once every year or two, the job eventually gets done somehow, and people have a maximal amount of time to forget the problem before the people who underfunded election administration have to face re-election themselves. If the local government doesn't hire enough people to count a very large number of ballots quickly (whatever that number may be), it is going to take much longer to count the ballots than it should. And, even if local governments don't deliberately underfund election administration, it is easy to accidentally underfund election administration if the official in charge of making that part of a local government budget is sufficiently incompetent and underestimates how many people will be needed for a job where worker productivity varies greatly from person to person and the number of ballots that need to be counted vary greatly from election to election.
Inevitably, somewhere, somehow, in the many 10s of thousands of precincts in the country, all of these things are going to happen at the same time and that precinct is going to lag behind all of the others in getting its votes counted.
For example, that is a pretty good description of the kinds of things that have delayed vote counting in Porter County, Indiana in this year's election.
In Maine, in a race where the first round results mean that rank choice voting applies, after the first round results are computed at the county or town level, all of the ballots are physically transported to the state capitol (Augusta) under armed guard, all of the ballots paper or otherwise are converted to a single uniform electronic format, and once that is done, a computer tabulates the results, a process that takes about three to four business days to accomplish.
Also, recall that unlike the U.K. and Canada, for example, where there is typically only a single issue or elective position to be decided on each ballot, in the U.S. most states have very long ballots. My ballot had approximately a dozen non-judicial candidate elections, a dozen judicial elections, and about a dozen ballot issues to resolve.
Counting ballots with three dozens data points each is much more arduous than counting ballots with a single question to resolve, particularly if it must be done manually, for example, because the computer system that is supposed to process the ballots isn't working properly (because, as most people know from common experience, computer systems that are only used once every year or two don't work properly due to technical or human error more often than 0.01% of the time).