The city is named for Nicholas and Elizabeth Jackson, landowners who deeded the land for the railroad right-of-way to the Cairo & Fulton Railroad in 1870. The community evolved from the settlement surrounding the railroad depot, eventually incorporating in 1941. In 1941, construction began on the Arkansas Ordinance Plant (AOP), which served as the primary facility for the development of fuses and denonators for World War II. Following the war, AOP ceased operations and the land was sold for commercial interests, including the development of the Little Rock Air Force Base in 1955. Today, portions of AOP still remain including the Arkansas Ordinance Plant Guard House which is on the National Register of Historic Places and the Jacksonville Museum of Military History. Despite Pulaski County being one of the few counties in Arkansas that is not a "dry" county, as it allows the sales of beer and liquor, the municipal limits of Jacksonville are "dry" as it does not allow the sales of alcohol in stores.
As of the census of 2000, there were 29,916 people, 10,890 households, and 8,004 families residing in the city. The population density was 1,134.2 people per square mile (437.9/km²). There were 11,890 housing units at an average density of 450.8/sq mi (174.0/km²). The racial makeup of the city was 64.17% White, 27.88% Black or African American, 0.50% Native American, 1.98% Asian, 0.13% Pacific Islander, 1.14% from other races, and 2.58% from two or more races. 6.24% of the population were Hispanic or Latino of any race.
There were 10,890 households out of which 40.2% had children under the age of 18 living with them, 55.1% were married couples living together, 14.6% had a female householder with no husband present, and 26.5% were non-families. 22.0% of all households were made up of individuals and 5.9% had someone living alone who was 65 years of age or older. The average household size was 2.64 and the average family size was 3.08.
In the city the population was spread out with 29.0% under the age of 18, 12.8% from 18 to 24, 33.2% from 25 to 44, 17.6% from 45 to 64, and 7.3% who were 65 years of age or older. The median age was 30 years. For every 100 females there were 100.4 males. For every 100 females age 18 and over, there were 98.4 males.
The median income for a household in the city was $35,460, and the median income for a family was $40,381. Males had a median income of $26,708 versus $21,804 for females. The per capita income for the city was $16,369. About 11.9% of families and 14.2% of the population were below the poverty line, including 20.5% of those under age 18 and 7.9% of those age 65 or over.