As of the 2020 census, there were 9,526 people, 3,957 households, and 2,513 families residing in the county.

At the 2010 census, there were 10,233 people, 4,027 households, and 2,798 families living in the county.

[14] In terms of ancestry, 10.7% were English, 10.2% were American, 10.2% were German, and 6.0% were Irish.

[17] At the 2000 census,[18] there were 9,958 people, 3,558 households and 2,604 families living in the county.

24.40% of all households were made up of individuals, and 10.20% had someone living alone who was 65 years of age or older.

Like most rural South Carolina counties with a tight Black-white population ratio, the Democratic Party has fared well in McCormick County compared to others across the South, especially with the national party's cultural turn to the left in the 2000s and 2010s.

However, in 2016 Donald Trump won the county by one fewer vote than Barack Obama did in 2012, marking the first GOP victory in the area since Richard Nixon in 1972.

[21] As of April 2024, some of the largest employers in the county include Food Lion, the United States Department of Defense, and the United States Postal Service.