According to the U.S. Census Bureau, the county has a total area of 701.58 square miles (1,817.1 km), of which 655.16 square miles (1,696.9 km) is land and 46.42 square miles (120.2 km) (6.62%) is water.

• Savannah National Wildlife Refuge (part)
• Tybee National Wildlife Refuge

• Frampton Plantation House
• Kingfisher Pond Recreation Area
• Old House Plantation
• Tillman Sand Ridge Heritage Preserve/Wildlife Management Area
• Turtle Island Wildlife Management Area

• Atlantic Ocean (North Atlantic Ocean)
• Intracoastal Waterway
• Little Black River
• Middle River
• Okatee River
• Savannah River
• Tulifiny River

• Hampton County – north
• Beaufort County – east
• Chatham County, Georgia – south
• Effingham County, Georgia – west

As of the 2020 census, there were 28,791 people, 10,269 households, and 7,298 families residing in the county.

At the 2010 census, there were 24,777 people, 8,517 households, and 5,944 families living in the county. The population density was 37.8 inhabitants per square mile (14.6 inhabitants/km). There were 10,299 housing units at an average density of 15.7 units per square mile (6.1 units/km). The racial makeup of the county was 46.0% black or African American, 43.0% white, 0.7% Asian, 0.5% American Indian, 0.1% Pacific islander, 8.3% from other races, and 1.4% from two or more races. Those of Hispanic or Latino origin made up 15.1% of the population. In terms of ancestry, 7.1% were Irish, and 2.5% were American.

Of the 8,517 households, 36.9% had children under the age of 18 living with them, 44.2% were married couples living together, 18.6% had a female householder with no husband present, 30.2% were non-families, and 24.8% of all households were made up of individuals. The average household size was 2.73 and the average family size was 3.23. The median age was 34.6 years.

The median income for a household in the county was $37,393 and the median income for a family was $45,800. Males had a median income of $31,999 versus $24,859 for females. The per capita income for the county was $17,997. About 14.2% of families and 21.5% of the population were below the poverty line, including 32.2% of those under age 18 and 14.5% of those age 65 or over.

At the 2000 census, there were 20,678 people, 7,042 households, and 5,091 families living in the county. The population density was 32 people per square mile (12 people/km). There were 7,928 housing units at an average density of 12 units per square mile (4.6 units/km). The racial makeup of the county was 52.69% Black or African American, 42.39% White, 0.37% Native American, 0.44% Asian, 0.05% Pacific Islander, 3.39% from other races, and 0.67% from two or more races. 5.75% of the population were Hispanic or Latino of any race.

There were 7,042 households, out of which 34.5% had children under the age of 18 living with them, 48.1% were married couples living together, 18.2% had a female householder with no husband present, and 27.7% were non-families. 23.2% of all households were made up of individuals, and 8.8% had someone living alone who was 65 years of age or older. The average household size was 2.75 and the average family size was 3.22.

In the county, the population was spread out, with 26.8% under the age of 18, 10.3% from 18 to 24, 30.7% from 25 to 44, 21.2% from 45 to 64, and 11.0% who were 65 years of age or older. The median age was 34 years. For every 100 females, there were 111.0 males. For every 100 females age 18 and over, there were 111.3 males.

The median income for a household in the county was $30,727, and the median income for a family was $36,793. Males had a median income of $29,407 versus $21,055 for females. The per capita income for the county was $14,161. About 15.4% of families and 20.7% of the population were below the poverty line, including 26.3% of those under age 18 and 21.4% of those age 65 or over.

Jasper County is governed by a five-member partisan county council, who are elected in staggered four year terms. The council appoints a county administrator who is tasked with running the day-to-day operations of the county, with the exception of the Sheriff's Office.

Mary Gordon Ellis, the first woman elected to the South Carolina legislature, represented Jasper County in the state senate for one term, from 1928 to 1932, after having served as state superintendent of schools.

Like most counties in the rural Black Belt of South Carolina, Jasper has long leaned Democratic. However, in 2024, Donald Trump was able to flip the county Republican for the first time since Richard Nixon carried it in 1972.

In 2022, the GDP was $1.7 billion (about $49,980 per capita), and the real GDP was $1.3 billion (about $39,745 per capita) in chained 2017 dollars.

As of April 2024, some of the largest employers in the county include AmeriGas, the city of Hardeeville, Publix, and Walmart.

• I-95
• US 17
• US 278
• 
  US 278 Conn.
• US 321
• US 601
• SC 3
• SC 46
• SC 170
• SC 315
• SC 336
• 
  SC 336 Conn.
• SC 462
• SC 652

CSX Transportation's Charleston Subdivision (also known as the Charleston-Savannah Railway) currently operates both freight trains and passenger trains (via Amtrak) along the line, but does not stop anywhere within the county. The line also runs along the Hampton-Jasper County border northeast of the bridge over the Tullifinny River.

Another active CSX line within the county is the Columbia Subdivision which bisects the northwest corner of Jasper County between the Georgia state line and Hampton County. This line also operates freight as well as Amtrak passenger trains.

• Hardeeville (largest community)

• Ridgeland (county seat)

• List of counties in South Carolina
• National Register of Historic Places listings in Jasper County, South Carolina
• Jasper Ocean Terminal, planned deepwater container port in the county

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

• Geographic data related to Jasper County, South Carolina at OpenStreetMap
• Official website
• Jasper County history and images