According to the U.S. Census Bureau, the county has a total area of 393.61 square miles (1,019.4 km), of which 358.87 square miles (929.5 km) is land and 34.74 square miles (90.0 km) (8.83%) is water. It is the smallest county in South Carolina by land area and second-smallest by total area. McCormick County is in the Savannah River basin.

• Sumter National Forest (part)

• Baker Creek State Park
• Eden Hall
• Hamilton Branch State Recreation Area
• Hickory Knob State Resort Park
• James L. Mason Wildlife Management Area
• Leroys Ferry Recreation Area
• Long Cane Creek Picnic Area
• Parksville Recreation Area
• Price's Mill
• Savannah Lakes Beach
• Stevens Creek Heritage Preserve/Wildlife Management Area (part)
• Sumter National Forest - Long Cane Ranger District

• J. Strom Thurmond Reservoir
• Savannah River
• Steven Creek

• Greenwood County – northeast
• Edgefield County – east
• Columbia County, Georgia – south
• Lincoln County, Georgia – west
• Elbert County, Georgia – northwest
• Abbeville County – northwest

• US 221
• US 378
• SC 10
• SC 23
• SC 28
• SC 81
• SC 283
• SC 823

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. The population density was 28.5 inhabitants per square mile (11.0/km). There were 5,453 housing units at an average density of 15.2 per square mile (5.9/km). The racial makeup of the county was 49.7% black or African American, 48.7% white, 0.3% Asian, 0.1% Pacific islander, 0.1% American Indian, 0.2% from other races, and 0.9% from two or more races. Those of Hispanic or Latino origin made up 0.8% of the population. In terms of ancestry, 10.7% were English, 10.2% were American, 10.2% were German, and 6.0% were Irish.

Of the 4,027 households, 21.0% had children under the age of 18 living with them, 50.4% were married couples living together, 15.2% had a female householder with no husband present, 30.5% were non-families, and 27.4% of all households were made up of individuals. The average household size was 2.22 and the average family size was 2.65. The median age was 50.0 years.

The median income for a household in the county was $35,858 and the median income for a family was $43,021. Males had a median income of $32,606 versus $28,067 for females. The per capita income for the county was $19,411. About 14.2% of families and 18.2% of the population were below the poverty line, including 37.6% of those under age 18 and 7.9% of those age 65 or over.

At the 2000 census, there were 9,958 people, 3,558 households and 2,604 families living in the county. The population density was 28 people per square mile (11 people/km). There were 4,459 housing units at an average density of 12 per square mile (4.6/km). The racial makeup of the county was 53.88% Black or African American, 44.78% White, 0.07% Native American, 0.29% Asian, 0.03% Pacific Islander, 0.38% from other races, and 0.57% from two or more races. 0.86% of the population were Hispanic or Latino of any race.

There were 3,558 households, out of which 24.80% had children under the age of 18 living with them, 51.80% were married couples living together, 17.60% had a female householder with no husband present and 26.80% were non-families. 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. The average household size was 2.39 and the average family size was 2.82.

In the county, the population was spread out, with 19.50% under the age of 18, 8.30% from 18 to 24, 27.60% from 25 to 44, 28.10% from 45 to 64 and 16.50% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 113.70 males. For every 100 females age 18 and over, there were 115.80 males.

The median income for a household in the county was $31,577, and the median income for a family was $38,822. Males had a median income of $28,824 versus $21,587 for females. The per capita income for the county was $14,770. About 15.10% of families and 17.90% of the population were below the poverty line, including 26.50% of those under age 18 and 11.90% of those age 65 or over.

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.

In 2022, the GDP was $278 million (about $27,961 per capita), and the real GDP was $222.8 million (about $22,410 per capita) in chained 2017 dollars.

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.

• McCormick (county seat and largest community)
• Parksville
• Plum Branch

• Clarks Hill
• Modoc
• Mount Carmel
• Willington

• Johnny Letman, musician
• Patrick Noble, governor of South Carolina (1838–1840)

• List of counties in South Carolina
• National Register of Historic Places listings in McCormick County, South Carolina

Wikimedia Commons has media related to McCormick County, South Carolina.

• Geographic data related to McCormick County, South Carolina at OpenStreetMap
• Official website