Santa Cruz is a county in southern Arizona, United States. As of the 2020 census, the population is 47,669. The county seat is Nogales. The county was established in 1899. It borders Pima County to the north and west, Cochise County to the east, and the Mexican state of Sonora to the south. Santa Cruz County includes the Nogales, Arizona Micropolitan Statistical Area, which is also included in the Tucson-Nogales, Arizona Combined Statistical Area.