As of the census of 2000, there were 13,120 people, 4,350 households, and 3,266 families residing in the county. The population density was 7 people per square mile (3/km²). There were 5,543 housing units at an average density of 3 per square mile (1/km²). The racial makeup of the county was 80.22% White, 0.54% Black or African American, 0.53% Native American, 0.11% Asian, 0.03% Pacific Islander, 15.46% from other races, and 3.11% from two or more races. 87.99% of the population were Hispanic or Latino of any race.
There were 4,350 households out of which 36.80% had children under the age of 18 living with them, 53.20% were married couples living together, 16.80% had a female householder with no husband present, and 24.90% were non-families. 22.90% of all households were made up of individuals and 11.70% had someone living alone who was 65 years of age or older. The average household size was 2.88 and the average family size was 3.40.
In the county, the population was spread out with 29.50% under the age of 18, 9.50% from 18 to 24, 26.40% from 25 to 44, 20.60% from 45 to 64, and 14.00% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 100.70 males. For every 100 females age 18 and over, there were 102.90 males.
The median income for a household in the county was $22,416, and the median income for a family was $26,014. Males had a median income of $25,601 versus $16,250 for females. The per capita income for the county was $11,324. About 23.00% of families and 27.20% of the population were below the poverty line, including 35.90% of those under age 18 and 25.30% of those age 65 or over.