2019-6-28 · Ajo (/ˈɑːhoʊ/ AH-hoh; O'odham: Moik Wahia or O'odham: ʼOʼoho) is a census-designated place (CDP) in Pima County, Arizona, United States. The population was 3,304 at the 2010 census. Ajo is located on State Route 85 just 43 miles (69 km) from the Mexican border. It is the closest community to Organ Pipe Cactus National Monument.