As of the census² of 2000, there were 49,063 people, 18,267 households, and 13,060 families residing in the county. The population density was 23/km² (60/mi²). There were 20,520 housing units at an average density of 10/km² (25/mi²). The racial makeup of the county was 58.67% White, 28.94% Black or African American, 0.23% Native American, 0.15% Asian, 0.07% Pacific Islander, 10.87% from other races, and 1.06% from two or more races. 15.14% of the population were Hispanic or Latino of any race.

There were 18,267 households out of which 33.20% had children under the age of 18 living with them, 52.20% were married couples living together, 14.20% had a female householder with no husband present, and 28.50% were non-families. 24.50% of all households were made up of individuals and 11.10% had someone living alone who was 65 years of age or older. The average household size was 2.63 and the average family size was 3.10.

The median income for a household in the county was $29,890, and the median income for a family was $34,760. Males had a median income of $26,212 versus $20,063 for females. The per capita income for the county was $14,499. About 15.30% of families and 19.40% of the population were below the poverty line, including 22.50% of those under age 18 and 22.70% of those age 65 or over.

Neighboring areas include the following: Wayne County, Lenoir County, Jones County, Onslow County, Pender County, and Sampson County. The cities and towns of Duplin County are Beulaville, Calypso, Faison, Greenevers, Harrells, Kenansville, Magnolia, Rose Hill, Teachey, Wallace, and Warsaw.