Nogales is a city in Santa Cruz County, Arizona, United States. The population was 20,878 at the 2000 census. According to 2005 Census Bureau estimates, the population of the city is 20,833. The city is the county seat of Santa Cruz County.Nogales, Arizona, borders the city of Nogales, Sonora, Mexico, and is Arizona's largest international border town. The southern terminus of Interstate 19 is located in Nogales at the U.S.-Mexico border; the highway continues south into Mexico as Mexico Federal Highway 15.Known in O'odham as Nowa:l, the name Nogales means "black walnuts" in Spanish, and the walnut trees which once grew abundantly in the mountain pass between the cities of Nogales, Arizona, and Nogales, Sonora, can still be found around the town.