The El Dorado Micropolitan Statistical Area includes all of Union County.
As of the census of 2000, there were 45,629 people, 17,989 households, and 12,646 families residing in the county. The population density was 44 people per square mile (17/km²). There were 20,676 housing units at an average density of 20 per square mile (8/km²). The racial makeup of the county was 66.15% White, 31.97% Black or African American, 0.24% Native American, 0.40% Asian, 0.01% Pacific Islander, 0.46% from other races, and 0.77% from two or more races. 1.14% of the population were Hispanic or Latino of any race.
There were 17,989 households out of which 32.20% had children under the age of 18 living with them, 51.30% were married couples living together, 15.20% had a female householder with no husband present, and 29.70% were non-families. 26.90% of all households were made up of individuals and 12.10% had someone living alone who was 65 years of age or older. The average household size was 2.48 and the average family size was 3.00.
In the county the population was spread out with 25.90% under the age of 18, 8.30% from 18 to 24, 27.00% from 25 to 44, 22.70% from 45 to 64, and 16.10% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 91.60 males. For every 100 females age 18 and over, there were 86.00 males.
The median income for a household in the county was $29,809, and the median income for a family was $36,805. Males had a median income of $31,868 versus $19,740 for females. The per capita income for the county was $16,063. About 14.70% of families and 18.70% of the population were below the poverty line, including 25.80% of those under age 18 and 14.30% of those age 65 or over.