The 2010 Japan Census forms will have been arriving in your post box over the last week and need to be completed and returned by October 7, 2010.
The Japanese language-only form is fairly straight forward and involves a multiple-choice form, rather like a Japanese university entrance examination. For information in English please visit the official census site. If you would like a survey in a language other than Japanese, either ask the visiting official (I did and was told she only had them in Japanese) or visit the your local ward office's Statistics & Election office in the General Administrative Section (総務課 souma-ka).
Japan conducts a national census every five years.