[4] It is named for James Hughes Callahan, an American soldier in the Texas Revolution.

Callahan County is included in the Abilene, Texas metropolitan statistical area.

According to the U.S. Census Bureau, the county has a total area of 901 square miles (2,330 km2), of which 899 sq mi (2,330 km2) are land and 1.9 sq mi (4.9 km2) (0.2%) are covered by water.

[5] Callahan Divide is range of hills that extends 26 miles (42 km) from west to southeast through Taylor and Callahan Counties, with highest elevation 2,411 ft (735 m), which together with other elevated areas in the two counties provide advantages in wind energy.

Per the 2010 United States census, Callahan County had 13,544 people.

Callahan County is part of the 71st district for elections to the Texas House of Representatives.