According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. It is the fourth-smallest county in New Mexico by area.
As of the 2000 census, there were 45,044 people, 16,766 households, and 11,870 families living in the county. The population density was 32 people per square mile. There were 19,212 housing units at an average density of 14 per square mile. The racial makeup of the county was 72.40% White, 6.86% Black or African American, 1.00% Native American, 1.78% Asian, 0.13% Pacific Islander, 14.08% from other races, and 3.75% from two or more races. 30.38% of the population were Hispanic or Latino of any race. There were 16,766 households out of which 38.00% had children under the age of 18 living with them, 54.00% were married couplesliving together, 12.80% had a female householder with no husband present, and 29.20% were non-families. 25.50% of all households were made up of individuals and 9.00% had someone living alone who was 65 years of age or older. The average household size was 2.62 and the average family size was 3.15. In the county, the population was spread out with 30.10% under the age of 18, 11.50% from 18 to 24, 28.80% from 25 to 44, 18.10% from 45 to 64, and 11.50% who were 65 years of age or older. The median age was 31 years. For every 100 females there were 97.60 males. For every 100 females age 18 and over, there were 94.30 males. The median income for a household in the county was $28,917, and the median income for a family was $33,900. Males had a median income of $25,086 versus $19,523 for females. The per capita income for the county was $15,049. About 15.50% of families and 19.00% of the population were below the poverty line, including 25.10% of those under age 18 and 14.30% of those age 65 or over.
2010 census
As of the 2010 census, there were 48,376 people, 18,015 households, and 12,341 families living in the county. The population density was. There were 20,062 housing units at an average density of. The racial makeup of the county was 69.7% white, 6.3% black or African American, 1.3% Asian, 1.2% American Indian, 0.1% Pacific islander, 17.2% from other races, and 4.1% from two or more races. Those of Hispanic or Latino origin made up 39.5% of the population. In terms of ancestry, 11.2% were German, 11.0% were American, 8.0% were Irish, and 6.7% were English. Of the 18,015 households, 37.8% had children under the age of 18 living with them, 49.0% were married couples living together, 14.2% had a female householder with no husband present, 31.5% were non-families, and 26.4% of all households were made up of individuals. The average household size was 2.63 and the average family size was 3.18. The median age was 31.5 years. The median income for a household in the county was $38,090 and the median income for a family was $48,933. Males had a median income of $35,743 versus $26,585 for females. The per capita income for the county was $19,925. About 15.5% of families and 20.1% of the population were below the poverty line, including 28.9% of those under age 18 and 13.5% of those age 65 or over.
