Ajo (pronounced /ɑːhoʊ/ ah-hoh) is a census-designated place (CDP) in Pima County, Arizona, United States. The population was 3,705 at the 2000 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.
Ajo is the Spanish word for garlic (Spanish pronunciation: [axo]). The Spanish aple may have named the place using the familiar word in place of the similar-sounding O'odham word for paint (ooho). The Tohono O'odham people obtained red paint pigments from the area.
Native Americans, Spaniards and Americans have all extracted mineral wealth from Ajo's abundant ore deposits. In the early nineteenth century, there was a Spanish mine nicknamed "Old Bat Hole" that was abandoned due to Indian raids. The first Anglo to pass through the Ajo area, Tom Childs, Sr., found the deserted mine complete with a 60-foot (18 m) shaft, mesquite ladders, and rawhide buckets in 1847. He did not stay long at that time, because he was on his way to the silver mines near Magdalena de Kino, Sonora.