There were slightly less than 2.2 million foreign nationals residing in Japan in 2009, according to Japan's Ministry of Justice. Since 2000, the foreign population grew by nearly half a million, from 1.7 million. Its share of the total Japan's population also increased from 1.3 percent in 2000 to 1.7 percent in 2009. (For comparison, the 38.5 million immigrants accounted for 12.5 percent of the total US population in 2009.)
The top five countries of origin for foreign nationals were China (31.1 percent or 680,518), North and South Korea (26.5 percent or 578,495), Brazil (12.2 percent or 267,456), the Philippines (9.7 percent or 211,716), and Peru (2.6 percent or 57,464). Together, these countries accounted for 82.1 percent of the 2,186,121 registered foreigners who lived in Japan as of 2009.
In terms of unauthorized immigrants, the Immigration Bureau estimated that about 91,000 people overstayed their visas, plus another 13,000 to 22,000 estimated to have entered the country without authorization. Together, they represented about 5 percent of the foreign nationals in Japan. (For comparison, the 11.2 million unauthorized immigrants accounted for 28 percent of the total US immigrant population in 2010.)
Nearly 40 percent of the 2.2 million foreigners resided in the Kanto region (which includes the Tokyo, Kanagawa, Chiba, Saitama, and Ibaragi prefectures), one of the most heavily affected regions by the March 11 earthquake.So, from this perspective it wouldn't take very many additional immigrants (temporary or permanent) to make a huge change in Japanese society. Admittedly, history suggests that this is unlikely to happen, but without such assistance, it may be difficult for Japan to climb out of the hole created by this disaster.