As the family settled in the western ("nishi" in Japanese) end of Imai Town, it followed the advice of Tadaakira MATSUDAIRA, the lord of Koriyama Castle and Ieyasu TOKUGAWA's grandson, and used "Imanishi" as a family name.
今井町の西口にあることから郡山城主徳川家康の孫松平忠明にすすめられて以後今西姓を名乗った。