Districts of Japan (郡#日本の郡) were areas of traditional local government in Japan before the Meiji period. The function of districts has changed over time, but they continue to exist in contemporary Japan.
Districts are not all the same size. They are roughly equivalent to a county in the United Kingdom or the United States. They are smaller than prefectures and larger than towns and villages.
Districts were established in the 8th century.
Until the 10th century, the chief government official of a district (gun) was called the gunji.  During the Edo period, the head of a district (gun) was called the gundai.
Between 1878 and 1921, the Meiji period and Taishō period, districts were given specific powers and responsibilities which are now diffused.