Ajo is a census-designated place 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 from the Mexican border. With its rich tradition as a former copper mining hub, Ajo is a casual town with relaxed charm. Enjoy it’s mild climate, low humidity and clear skies. Take in the historic Spanish Colonial Revival architecture, Sonoran Desert flora and fauna and panoramic views.