Shinpei ETO was born in Yae Village, Saga District, Hizen Province (present-day Nabeshima-cho, Saga City, Saga Prefecture) as the eldest son of Tanemitsu ETO and Asako.
肥前国佐賀郡八戸村（現在の佐賀県佐賀市鍋島町）に佐賀藩藩士の江藤胤光・浅子の長男として生まれる。