[2] Per Japanese census data,[5] the population of Ōtsuki has declined at an accelerating rate in recent decades.

During the Edo period, all of Kai Province was tenryō territory under direct control of the Tokugawa shogunate, although the portion around modern day Ōtsuki was part of the short-lived Tamimura Domain, which was suppressed in 1704.

During the cadastral reform of the early Meiji period on July 1, 1889, the village of Hirosato was created within Kitatsuru District, Yamanashi Prefecture.

The town was bombed by the United States on August 13, 1945, only two days before the end of World War II.

Ōtsuki has a mayor-council form of government with a directly elected mayor and a unicameral city legislature of 12 members.