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.

He did not stay long at that time, because he was on his way to the silver mines near Magdalena de Kino, Sonora.

Thirty-five years later, Childs and his son returned with a friend and started developing the abandoned mine.

Soon the Arizona Mining & Trading company, formed by Peter R. Brady, a friend of Childs, worked the rich surface ores, shipping loads around Cape Horn for smelting in Swansea, Wales, in the mid-1880s.

Long supply lines and the lack of water discouraged large mining companies With the advent of new recovery methods for low-grade ore, Ajo boomed.

He became general manager of the Calumet and the Arizona mining company and expanded it on a grand scale.

[4] Ajo is home to many retired people, Border Patrol agents, and young families.

During the construction of a new border wall in 2019–2020, many workers lived in the RV parks, hotels and rental houses.

[5] According to the United States Census Bureau, the census-designated place has a total area of 28.1 square miles (72.8 km2), all land.

[7] This area has a large amount of sunshine year round due to its stable descending air and high pressure.

[8] Rainfall is very low except during occasional monsoonal or frontal incursions, and is especially minimal between April and June.

[9] Temperatures are very hot from April to October and mild to warm from November to March, with extremes ranging from 17 °F (−8 °C) on January 22, 1937, during that month's record Western cold wave, to 120 °F (49 °C) on July 20, 2023.

[14] With the combination of all county precincts into 3 districts in 1940, it did not formally appear again until 1950, when it reported as an unincorporated village.