As of the 2000 census, there were 18,018 people, 6,639 households, and 4,541 families living in the county. The population density was 7 people per square mile. There were 7,746 housing units at an average density of 3 per square mile. The racial makeup of the county was 74.14% White, 1.65% Black or African American, 1.10% Native American, 0.62% Asian, 0.07% Pacific Islander, 19.76% from other races, and 2.65% from two or more races. 33.29% of the population were Hispanic or Latino of any race. There were 6,639 households out of which 35.50% had children under the age of 18 living with them, 53.00% were married couplesliving together, 11.70% had a female householder with no husband present, and 31.60% were non-families. 24.70% of all households were made up of individuals and 9.10% had someone living alone who was 65 years of age or older. The average household size was 2.60 and the average family size was 3.14. In the county, the population was spread out with 28.10% under the age of 18, 16.00% from 18 to 24, 25.50% from 25 to 44, 18.30% from 45 to 64, and 12.10% who were 65 years of age or older. The median age was 30 years. For every 100 females there were 96.50 males. For every 100 females age 18 and over, there were 93.50 males. The median income for a household in the county was $26,586, and the median income for a family was $31,813. Males had a median income of $26,170 versus $20,684 for females. The per capita income for the county was $14,185. About 17.30% of families and 22.70% of the population were below the poverty line, including 25.10% of those under age 18 and 16.80% of those age 65 or over.
2010 census
As of the 2010 census, there were 19,846 people, 7,299 households, and 4,671 families living in the county. The population density was. There were 8,163 housing units at an average density of. The racial makeup of the county was 76.9% white, 1.8% black or African American, 1.3% American Indian, 0.9% Asian, 15.9% from other races, and 3.2% from two or more races. Those of Hispanic or Latino origin made up 39.9% of the population. In terms of ancestry, 12.7% were German, 10.0% were American, 9.8% were English, and 9.3% were Irish. Of the 7,299 households, 35.6% had children under the age of 18 living with them, 47.3% were married couples living together, 11.7% had a female householder with no husband present, 36.0% were non-families, and 28.3% of all households were made up of individuals. The average household size was 2.57 and the average family size was 3.20. The median age was 29.7 years. The median income for a household in the county was $37,762 and the median income for a family was $43,536. Males had a median income of $37,719 versus $21,916 for females. The per capita income for the county was $16,933. About 16.0% of families and 22.8% of the population were below the poverty line, including 25.6% of those under age 18 and 14.3% of those age 65 or over.
