First minted in 1869, the yen was adopted as Japan‘s official monetary unit on this day in 1871 when the government suspended the exchange of clan notes, money issued by feudal lords that had circulated since the 16th century. (According to a Ministry of Finance survey of 1868, a total of 1,694 denominations of clan money had been issued by 244 clans, 14 magistrates’ offices, and 9 shogunate retainers during the Tokugawa period [1603–1867].) By 1879 the replacement of clan notes by the yen-based government notes had been completed.
– britannica.com