Japan’s population has contracted by a record 3.09 million people over the past five years, preliminary 2025 census data show, accelerating a demographic decline that is reshaping the world’s fourth-largest economy. The total number of residents, including foreign nationals, stood at 123,049,524 as of October last year, a drop of 2.5 per cent from 2020. The pace of loss has nearly quadrupled compared with the previous quinquennial survey, when the population slipped by just 0.7 per cent. “The data has confirmed yet again that our country’s population decline is worsening,” Chief Cabinet Secretary Minoru Kihara told reporters. All but two of Japan’s 47 prefectures lost inhabitants; Tokyo and Okinawa were the sole exceptions, while even suburban commuter belts such as Saitama, Chiba and Kanagawa, which had previously bucked the trend, recorded absolute falls.

Behind the headline figure lies an entrenched structural crisis. Japan already has the oldest population in the world after Monaco, and its fertility rate of 1.2 children per woman is far below the 2.1 needed for natural replacement. The 2025 survey attributes the entire decline to natural decrease—deaths outstripping births by a widening margin—with net migration providing no offset. The census also revealed that the greater Tokyo metropolitan area now accounts for more than 30 per cent of all residents for the first time, a concentration that leeches vitality from the regions and complicates balanced national development.

The political fallout is immediate. The census serves as the basis for redrawing electoral constituencies, and the preliminary count has produced vote-value disparities of up to 2.274 times between the most and least populous lower house districts. Thirty-nine single-seat constituencies exceed the two-to-one threshold that the Supreme Court has signalled as the limit of constitutionality. A government council is expected to propose new boundaries by May 2027, but the task of reconciling equal suffrage with depopulation will only grow more fraught as the countryside empties.

Social initiatives to reverse the trend remain limited in scale. In a symbolic move, Shoko Kawata, mayor of Yawata in Kyoto Prefecture and the youngest female mayor in Japanese history, is due to become the first sitting mayor to take maternity leave, seeking to normalise child-rearing in public office. Yet the broader context is stark: nationwide births fell to an estimated 705,809 in 2025, a historic low. While immigration is often advanced as a policy remedy, the government’s response has so far focused on “comprehensive measures” to raise birth rates and support families, with no significant shift toward opening the country to large-scale foreign labour.

Japan’s predicament is a harbinger for other ageing societies. Without a sustained reversal in fertility or a recalibration of immigration policy, the labour force will continue to shrink, social security costs will mount, and the political geography of the country will become ever more distorted. The census has laid bare the mathematics; the difficult choices remain politically and culturally deferred.