Mizhi is situated in the Loess Plateau on the banks of Wuding River.

The county is established in 1226, named after Mizhizhai (Mizhi Stockade).

It was renamed Tianbao in about 1643 by Li Zicheng, but was restored as Mizhi soon.

Li had additionally built his temporary palace in the county.

During the second Sino-Japanese war, it was administered by the Shaanxi-Gansu-Ningxia Border Region government.