"According to a government survey, 1.1 percent of children born in Japan were illegitimate in 1990, but the rate rose to 2.2 percent in 2011. The number of "unmarried mothers" nearly doubled to 132,000 in 2010 from 63,000 in 2000."
Source:
Supreme Court set to decide on inheritance rights of illegitimate children
August 29th 2013
Mainchi Shimbun Japan
http://mainichi.jp/english/english/newsselect/news/20130829p2a00m0na012000c.html