In the Nebraska license plate system, Nuckolls County is represented by the prefix 42 (it had the forty-second-largest number of vehicles registered in the county when the license plate system was established in 1922).
1860 - 22 1870 - 8 1880 - 4,235 1890 - 11,417 1900 - 12,414 1910 - 13,019 1920 - 13,236 1930 - 12,629 1940 - 12,781 1950 - 10,973 1960 - 8,217 1970 - 7,404 1980 - 6,726 1990 - 5,786 2000 - 5,057
As of the census of 2000, there were 5,057 people, 2,218 households, and 1,443 families residing in the county. The population density was 9 people per square mile (3/km²). There were 2,530 housing units at an average density of 4 per square mile (2/km²). The racial makeup of the county was 98.91% White, 0.02% Black or African American, 0.06% Native American, 0.16% Asian, 0.53% from other races, and 0.32% from two or more races. 1.01% of the population were Hispanic or Latino of any race.
There were 2,218 households out of which 26.50% had children under the age of 18 living with them, 58.80% were married couples living together, 4.60% had a female householder with no husband present, and 34.90% were non-families. 32.30% of all households were made up of individuals and 18.00% had someone living alone who was 65 years of age or older. The average household size was 2.26 and the average family size was 2.86.
In the county the population was spread out with 23.40% under the age of 18, 5.40% from 18 to 24, 22.50% from 25 to 44, 24.30% from 45 to 64, and 24.40% who were 65 years of age or older. The median age was 44 years. For every 100 females there were 92.50 males. For every 100 females age 18 and over, there were 91.90 males.
The median income for a household in the county was $28,958, and the median income for a family was $35,018. Males had a median income of $24,533 versus $17,806 for females. The per capita income for the county was $15,608. About 6.50% of families and 11.20% of the population were below the poverty line, including 16.70% of those under age 18 and 8.90% of those age 65 or over.