As of the 2000 census, there were 30,126 people, 11,134 households, and 7,537 families living in the county. The population density was 6 people per square mile. There were 14,254 housing units at an average density of 3 per square mile. The racial makeup of the county was 56.22% White, 0.78% Black or African American, 1.82% Native American, 0.54% Asian, 0.08% Pacific Islander, 36.21% from other races, and 4.33% from two or more races. 77.96% of the population were Hispanic or Latino of any race. There were 11,134 households out of which 34.60% had children under the age of 18 living with them, 44.50% were married couplesliving together, 16.40% had a female householder with no husband present, and 32.30% were non-families. 26.60% of all households were made up of individuals and 8.20% had someone living alone who was 65 years of age or older. The average household size was 2.58 and the average family size was 3.10. In the county, the population was spread out with 27.40% under the age of 18, 10.90% from 18 to 24, 27.00% from 25 to 44, 22.90% from 45 to 64, and 11.70% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 96.70 males. For every 100 females age 18 and over, there were 93.90 males. The median income for a household in the county was $26,524, and the median income for a family was $31,250. Males had a median income of $27,307 versus $22,588 for females. The per capita income for the county was $13,268. About 19.90% of families and 24.40% of the population were below the poverty line, including 27.80% of those under age 18 and 25.90% of those age 65 or over.
2010 census
As of the 2010 census, there were 29,393 people, 11,978 households, and 7,275 families living in the county. The population density was. There were 15,595 housing units at an average density of. The racial makeup of the county was 66.6% white, 1.7% American Indian, 1.4% black or African American, 0.8% Asian, 0.1% Pacific islander, 25.4% from other races, and 3.9% from two or more races. Those of Hispanic or Latino origin made up 76.8% of the population. In terms of ancestry, 6.3% were German, 5.3% were English, and 1.6% were American. Of the 11,978 households, 28.8% had children under the age of 18 living with them, 38.6% were married couples living together, 14.9% had a female householder with no husband present, 39.3% were non-families, and 32.5% of all households were made up of individuals. The average household size was 2.34 and the average family size was 2.95. The median age was 40.7 years. The median income for a household in the county was $32,213 and the median income for a family was $42,888. Males had a median income of $35,176 versus $28,351 for females. The per capita income for the county was $18,508. About 15.7% of families and 24.8% of the population were below the poverty line, including 29.6% of those under age 18 and 22.7% of those age 65 or over.
San Miguel County is heavily Democratic. The last time it voted Republican for president was 1956, and since 1992 no Republican has cracked 30% of the vote.
