Jefferson County is a county located in the U.S. state of Mississippi; its western border is formed by the Mississippi River. As of the 2010 census, the population was 7,726, making it the third-least populous county in Mississippi. Its county seat is Fayette. The county is named for U.S. President Thomas Jefferson.
According to the U.S. Census Bureau, the county has a total area of 527 square miles (1,360 km), of which 520 square miles (1,300 km) is land and 7.3 square miles (19 km) (1.4%) is water.
As of the 2010 United States Census, there were 7,726 people residing in the county. 85.7% were Black or African American, 13.7% White, 0.2% Native American and 0.3% of two or more races. 0.4% were Hispanic or Latino (of any race).
As of the census of 2000, there were 9,740 people, 3,308 households, and 2,338 families residing in the county. The population density was 19 people per square mile (7/km²). There were 3,819 housing units at an average density of 7 per square mile (3/km²). The racial makeup of the county was 13.06% White, 86.49% Black or African American, 0.08% Native American, 0.10% Asian, 0.01% Pacific Islander, 0.02% from other races, and 0.24% from two or more races. 0.66% of the population were Hispanic or Latino of any race. Jefferson County has the highest percentage of black residents of any U.S. county.
There were 3,308 households out of which 36.60% had children under the age of 18 living with them, 36.00% were married couples living together, 28.50% had a female householder with no husband present, and 29.30% were non-families. 27.10% of all households were made up of individuals and 10.10% 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 3.36.
In the county, the population was much younger than the national average with 28.80% under the age of 18, 12.10% from 18 to 24, 28.50% from 25 to 44, 19.60% from 45 to 64, and 10.90% who were 65 years of age or older. The median age was 32 years. For every 100 females there were 99.00 males. For every 100 females age 18 and over, there were 99.00 males.
The median income for a household in the county was $18,447, and the median income for a family was $23,188. Males had a median income of $25,726 versus $18,000 for females. The per capita income for the county was $9,709. About 32.50% of families and 36.00% of the population were below the poverty line, including 46.00% of those under age 18 and 34.40% of those age 65 or over.
In 2009, Jefferson County has the lowest per capita income in Mississippi and the 17th lowest in the United States.