Sakura Domain
Hayashi was born in Sakura city, Shimōsa Province (present-day Chiba prefecture), as the son of Satō Taizen, a physician practising "Dutch medicine" for the Sakura Domain. He was adopted as a child by Hayashi Dokai, a physician in the service of the Tokugawa shogunate, from whom he received the family name "Hayashi", but he sometimes referred to himself as "Satō Tosaburō". He learned English at the Hepburn Academy in Yokohama (the forerunner of Meiji Gakuin University).