Although immigration to Japan has been subtle and slow, Japan is becoming home to more and more visible immigrant communities, with residential segregation and ethnic communities establishing more visible identities in Japan. This is due not only to increasing immigration but also to the consequent increase of the descendants of immigrants and the increase of intermarriages and mixed children born in such unions. Despite the change in the population, the current Population Census fails to capture the diversity that exists in contemporary Japanese society. The census and statistical classification needs to be modified to reflect the changes in the population and to acknowledge the new generation of diverse Japanese, together with the discussion of what it means to be Japanese. This chapter will first briefly introduce the Japanese census categories from 1920 onwards. It will then highlight the invisibility of race, ethnicity, and mixed categories in the contemporary Japanese census category of nationality, and how this is connected to the perceptions of mixed persons in Japan. We argue that there is a need for further discussion and we propose ways of incorporating classifications of race, ethnicity, and mixed categories into the Population Census in the future.