According to the United States Census Bureau, the county has a total area of, of which is land and is water. The county contains rolling hills and knolls, sloped to the southeast. It is drained by the Atascosa River which exits the county at its SE corner. The highest point is a localized hill near the northeast border with Bexar County, between Lytle and Somerset in Bexar, at 810 feet ASL.
As of the 2010 United States Census, there were 44,911 people 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. 61.9% were Hispanic or Latino. As of the 2000 United States Census, there were 38,628 people, 12,816 households, and 10,022 families in the county. The population density was 31/sqmi. There were 14,883 housing units at an average density of 12/sqmi. The racial makeup of the county was 73.23% White, 0.60% Black or African American, 0.80% Native American, 0.31% Asian, 0.06% Pacific Islander, 21.53% from other races, and 3.47% from two or more races. 58.56% of the population were Hispanic or Latino of any race. There were 12,816 households out of which 41.70% had children under the age of 18 living with them, 60.30% were married couplesliving together, 13.00% had a female householder with no husband present, and 21.80% were non-families. 18.90% of all households were made up of individuals and 8.70% had someone living alone who was 65 years of age or older. The average household size was 2.99 and the average family size was 3.41. The county population contained 31.70% under the age of 18, 8.90% from 18 to 24, 27.60% from 25 to 44, 21.00% from 45 to 64, and 10.80% who were 65 years of age or older. The median age was 32 years. For every 100 females, there were 96.60 males. For every 100 females age 18 and over, there were 94.20 males. The median income for a household in the county was $33,081, and the median income for a family was $37,705. Males had a median income of $27,702 versus $18,810 for females. The per capita income for the county was $14,276. About 16.10% of families and 20.20% of the population were below the poverty line, including 25.60% of those under age 18 and 21.70% of those age 65 or over.
Education
The following school districts serve Atascosa County:
