As of the census of 2000, there were 20,047 people, 7,855 households, and 5,317 families residing in the county. The population density was 41 people per square mile (16/km²). There were 8,793 housing units at an average density of 18 per square mile (7/km²). The racial makeup of the county was 71.76% White, 26.23% Black or African American, 0.25% Native American, 0.27% Asian, 0.01% Pacific Islander, 0.62% from other races, and 0.85% from two or more races. Approximately 1.57% of the population were Hispanic or Latino of any race. Among the major first ancestries reported in Pemiscot County were 31.9% American, 7.8% Irish, 5.6% English, and 5.5% German, according to Census 2000.
There were 7,855 households out of which 33.60% had children under the age of 18 living with them, 45.00% were married couples living together, 18.50% had a female householder with no husband present, and 32.30% were non-families. 28.80% of all households were made up of individuals and 14.30% had someone living alone who was 65 years of age or older. The average household size was 2.52 and the average family size was 3.10.
In the county the population was spread out with 30.00% under the age of 18, 9.10% from 18 to 24, 25.00% from 25 to 44, 21.10% from 45 to 64, and 14.90% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 88.50 males. For every 100 females age 18 and over, there were 83.30 males.
The median income for a household in the county was $26,992, and the median income for a family was $33,945. Males had a median income of $27,476 versus $17,358 for females. The per capita income for the county was $15,599. About 24.80% of families and 30.40% of the population were below the poverty line, including 43.20% of those under age 18 and 23.20% of those age 65 or over.