The town of Mitsukaidō was established within Toyoda District with the creation of the modern municipalities system on April 1, 1889.

On July 10, 1954 Mitsukaidō merged with the villages of Sugawara, Ohanawa, Mitsuma, Goka, Ono and Sakate, and was elevated to city status.

On January 1, 2006, Mitsukaidō absorbed the neighboring town of Ishige, Yūki District, Ibaraki and officially changed their name to Jōsō.

Jōsō has a mayor-council form of government with a directly elected mayor and a unicameral city council of 22 members.

In terms of national politics, the city is part of Ibaraki 7th district of the lower house of the Diet of Japan.