[3] As of the 2000 census,[9] there were 13,270 people, 6,113 households, and 3,618 families living in the county.

The racial makeup of the county was 86.97% White, 0.48% Black or African American, 1.48% Native American, 0.17% Asian, 0.08% Pacific Islander, 8.27% from other races, and 2.54% from two or more races.

35.90% of all households were made up of individuals, and 19.30% had someone living alone who was 65 years of age or older.

As of the 2010 census, there were 11,988 people, 5,917 households, and 3,126 families living in the county.

[10] In terms of ancestry, 14.0% were German, 9.4% were American, 8.4% were English, and 8.0% were Irish.

[14] Spaceport America is located in Sierra County, 45 miles (72 kilometers) north of Las Cruces and 30 miles (48 kilometers) east of Truth or Consequences.

Sierra County voters approved the creation of a spaceport tax district in April 2008, freeing up funding for its construction.

On May 22, 2021, Virgin Galactic's VSS Unity launched from the spaceport with three people aboard becoming the first crewed launch from both Spaceport America and New Mexico and making New Mexico the third U.S. state, after California and Florida, to send humans into space.