As part of a series of ongoing projects on migration and populism (see e.g. here), I happened to come across a report from the 2010 Japanese Census. It contains data on Japan’s foreign population since 1950, and how it has changed. A couple of quick plots of these data are remarkably revealing.

First, look at the changes in numbers. Japan’s population was well under 1% foreign until the 1980s, when you see a large jump corresponding to the post-oil crisis reforms to Japanese citizenship laws and continuing into the Lost Decade.

At the same time, the sex ratio basically flips, but gradually rather than discontinuously with the 1980s reforms. The sex ratio among foreigners living in Japan was basically 1.2 men for every woman in 1950, and it is now closer to 0.8 men for every woman.

Who are these foreigners? We can break out the trends by nationality:

For most of the twentieth century, Koreans have comprised by far the largest population of foreigners in Japan. That proportion declined precipitously in the 1980s, as a result of two processes. First, the above-mentioned citizenship reforms. But second, the gradual naturalization of Japanese of Korean descent (previously counted among the foreigners). So this reversal is partially due to higher relative immigration by non-Koreans, and partially due to composition effects. What is most striking is the increase in “Others,” comprised partially of Brazilians and Peruvians (the dekasegi) but also Southeast and South Asians.

Japan still has a far smaller immigrant population than nearly all other OECD countries. But Japan is no longer the mono-ethnic society, closed to foreigners, that it once was. But unlike the initial years of labor migration into Western Europe after WWII, women rather than men are leading the way. That is interesting, and it probably will have political consequences.