Ajo ( AH-hoh; O'odham: Moik Wahia or O'odham: ʼOʼoho) is an unincorporated community in Pima County, Arizona, United States. It is the closest community to Organ Pipe Cactus National Monument. 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.
Ajo is the Spanish word for garlic (Spanish pronunciation: [ˈaxo]). The Spanish may have named the place using the familiar word in place of the similar-sounding O'odham word for paint (oʼoho). 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. Tom Childs, Sr., found the deserted mine complete with a 60-foot (18 m) shaft, mesquite ladders, and rawhide buckets in 1847.