As of October 1, 2007, the population of Tokyo is estimated to be 12.790 million, or about 10% of Japan's total population, and it has the largest population among all the 47 prefectures.

At 2,187 square kilometers, the area of Tokyo is 0.6% of the total area of Japan, making it the third smallest of Japan's 47 prefectures. With a population density of 5,847 persons per square kilometer, Tokyo is the most densely populated prefecture in Japan.The 23 special-ward area is home to 8.653 million persons, the Tama area 4.109 million, and the Islands 28,000. Tokyo has 6.088 million households, with an average 2.10 persons per household. The number of registered foreign residents reached 386,000 as of October 1, 2007, some 1.4 times more than the total figure ten years earlier.

 The population of Tokyo might break 13 million as early as next year, five years earlier than estimated by the national population research institute and the Tokyo Metropolitan Government, because the capital has become a magnet for people fleeing sluggish economies in the rest of Japan.According to estimates made in May 2007 by the National Institute of Population and Social Security Research, the population of Tokyo will climb to 12.9 million in 2010 and peak at 13.1 million in 2020 before sliding back to 13.04 million in 2025. In March, the government of Tokyo predicted the population would grow to 13.08 million in 2015 before falling to 12.94 million in 2020.But the actual population has been increasing at an annual rate of around 100,000 since 2000. As of Dec. 1 this year, it stood at 12.9 million, the same as the institute's earlier estimate for 2010, due to a net yearly increase of some 70,000. "We may have underestimated the pace of the population growth," said a statistician at the Tokyo government. While Japan's overall population is decreasing with the aging of society and a fall in the birthrate, the accelerating concentration of people in Tokyo could sap local economies of vital energy.Okinawa, located far from the four main islands, used to attract a significant number of new residents from the rest of Japan, including baby boomers born in the late 1940s, because of its unique culture and for other reasons.But the prefecture saw a net decrease in its population in 2006. In light of this, Moritake Tomikawa, president of Okinawa International University, believes that the population of Okinawa will decline after peaking in 2010, 15 years earlier than forecast by the national institute.Because of the high unemployment rate in Okinawa, young people are leaving, Tomikawa said. "We urgently need to promote tourism and other local industries." Source