Hirota was born in in what is now part of Chūō-ku, Fukuoka city, Fukuoka Prefecture. His father was a stonemason whose family name was Tokubei (徳平), and who was adopted into the Hirota family. Tokubei married Take (タケ), a daughter of the president of a Japanese noodle company. On 14 February 1878, the couple had a son, whom Tokubei named . They later had three more children. Tokubei's name is engraved on the epigraph which recognized masons who contributed to the construction of a statue of Emperor Kameyama in Higashi kōen (東公園) in Fukuoka city.