1. The Short Answer: One Clear Rule, Secret Answers and Several Ways to Reply
Japan's Statistics Bureau counts people who "usually live" in the country, and that includes foreign residents. A person is counted at the home where they have lived for three months or more, or where they are going to live [1]. Special rules cover the cases where that sentence is not enough, such as boarding students, long hospital stays and ship crews. Those rules are there so that nobody is counted twice, or missed entirely. Answers are only useful if people give them, so the system also promises secrecy, with prison terms and fines for staff who leak answers [3], and it lets households reply in several ways. In 2025, nearly half of households replied on the internet [5]. The next sections take these three ideas one at a time.
2. Who Counts as "Everyone", and Where Is a Student Counted?
The rule is written in the Statistics Bureau's outline of the census. In the 2020 census, "usually living" meant living in a home for three months or more, or being due to live there. A person with no such home was counted where they were at the time of the census [1]. Foreign residents were included. Two groups were left out: members of foreign diplomatic missions and consulates and their families, and foreign military personnel and their families [1].
Then come the exceptions, which are the interesting part. A student who stays in a dormitory or boarding house to go to school is counted at that lodging, not at the family home. A person who has been in a hospital or clinic for three months or longer is counted at the hospital, while people with shorter or uncertain stays are counted at home. A sailor on a ship with no home on land is counted on the ship [1]. Because the rule picks exactly one place for each person, a student cannot be counted once by the parents and again by the dorm. Reading the Bureau's text, this looks like the purpose of the exceptions. The text lists the exceptions but does not spell out the reasons, so that part is our interpretation. The 2025 outline, the one for the latest census, describes the same idea of "usually living" in similar words [2].
3. Why Do People Trust the Census With Their Answers?
A clear counting rule is not enough if people are afraid to answer. The Statistics Bureau explains that everyone who works on the census, and everyone who has worked on one in the past, is bound by a duty of secrecy. Revealing a secret can be punished by up to two years in prison or a fine of up to one million yen [3]. The Bureau says the purpose is to let people answer every question without worry. The answers are used only to make statistics, and the Bureau states that they are never used for other purposes such as tax checks. Completed forms are stored carefully and are dissolved completely after the figures have been compiled [3].
The routes for sending answers are also built around privacy. In a Bureau Q&A about a trial survey held before the 2025 census, online answers go straight to the ministry's server and mailed forms go to a post-office box set up by the ministry, so the local census worker never sees them. A household can also hand the form to the worker in a sealed envelope, which the worker passes on to the city office without opening [4]. That Q&A describes a trial survey, so the real 2025 census may differ in detail. It shows the design idea, which is that the person who knocks on your door does not need to read your answers.
4. How Many Households Answered Online, by Mail and in Person?
The Bureau lets households answer on the internet, by mail, or by handing the form to a census worker [2]. Its response table for the 2025 census has 57,324,619 households in the basic population count. Of those, 27,149,428 answered on the internet and 18,905,587 by mail [5]. Dividing by the number of households gives about 47.4% online and 33.0% by mail. Together, that is about 80.4% of households. The remaining one-fifth or so are not broken down in the part of the table we could read, so we cannot say exactly how they replied. It probably includes forms handed to workers, but that is a guess.
For comparison, the United States Census Bureau says its 2020 census was the first in which all households were invited to respond online [6]. Several countries have been adding internet options in recent years, so Japan's mix of three routes is part of a wider pattern. The basic idea is that more ways to answer can give more people an option that suits them.
5. When Did Japan Hold Its First Census, and How Long Did It Take to Prepare?
The first national census in Japan was held on October 1, 1920, and it counted 55,963,053 people [7]. A law about holding a census had been passed 18 years earlier, in 1902. The Bureau notes that this was 130 years after the 1790 census in the United States, which it calls the first of the modern censuses [7]. A budget for the first census was approved in March 1918, and the date was set for 1920 [7]. Counting from 1920, the 2025 census was the 22nd [2]. The outline for 2020 called that year the 21st and a milestone of 100 years since the first [1].
6. Try the Rule: Where Would You Be Counted in These Cases?
Reading a rule is different from using it. Try these three cases on paper, then check them against section 2. A university student rents a room near their university and goes home only for holidays. A person is staying in a hospital for four months. A person has lived in a house for six years and is away on a two-week trip on census day. The answers follow the rules above, and the Bureau's own pages are the place to confirm them [1]. Whichever way you answer, notice that the rule always ends with one place for each person. If you want to learn more, your own country's census office probably has a similar page about who is counted and where.