[3][4] Atascosa County is part of the San Antonio-New Braunfels metropolitan statistical area.

[5] The county contains rolling hills and knolls, sloped to the southeast.

It is drained by the Atascosa River, which exits the county at its southeastern corner.

[7] As of the 2010 United States census, 44,911 people resided in the county; 84.9% were White, 0.8% Black or African American, 0.8% Native American, 0.3% Asian, 0.1% Pacific Islander, 10.9% of some other race, and 2.3% of two or more races.

As of the 2000 United States census,[13] 38,628 people, 12,816 households, and 10,022 families were in the county.

The 14,883 housing units had an average density of 12 per square mile (4.6/km2).