Youyu County, also known by its Chinese name Youyuxian, is a county under the administration of the prefecture-level city of Shuozhou, in the northwest of Shanxi Province, China. It borders Inner Mongolia to the north and west.

Shanwu,^[2] south of present-day Youyuxian, was the seat of Yanmen Commandery during the Qin and Western Han.^[3] The post moved to Yinguan southeast of present-day Shuozhou under the Eastern Han and further south to Daixian under the Kingdom of Wei.^[2]

Elevations are generally higher in the south of the county, in which flows the Cangtou River (苍头河); Youyu reaches a north-south extent of 67.7 km (42.1 mi) and east-west width of 45.7 km (28.4 mi). The Great Wall demarcates the northwestern border with Inner Mongolia's Liangcheng and Horinger counties; within the province, Youyu borders Zuoyun County to the east, Shanyin County and Pinglu District to the south.