Mianchi County is a county under the jurisdiction of the prefecture-level city of Sanmenxia, in the northwest of Henan province, bordering Shanxi province to the north and northwest. Its population in 2019 was 353,200.

Sanmenxia is a prefecture-level city in the west of Henan Province, China. The westernmost prefecture-level city in Henan, Sanmenxia borders Luoyang to the east, Nanyang to the southeast, Shaanxi Province to the west and Shanxi Province to the north. The city lies on the south side of the Yellow River at the point where the river cuts through the Loess Plateau on its way to the North China Plain.