[2] The county takes its name from the Mexican Spanish name of the Purgatoire River, originally called El Río de las Ánimas Perdidas en el Purgatorio, which means "River of the Lost Souls in Purgatory.

At the 2000 census there were 15,207 people, 6,173 households, and 4,092 families living in the county.

A Democratic stronghold since the days of Franklin Roosevelt after having been solidly Republican during the "system of 1896" like the rest of Hispanic Colorado, Las Animas County has seen a strong trend toward the Republican Party in recent elections.

Hillary Clinton's 2016 performance was the worst by a Democrat since John W. Davis in 1924.

In 2020, Joe Biden became the first Democrat to win the presidency without the county since Woodrow Wilson in 1912.