In the Nebraska license plate system, Harlan County is represented by the prefix 51 (it had the fifty-first-largest number of vehicles registered in the county when the license plate system was established in 1922).
1880 - 6,086 1890 - 8,158 1900 - 9,370 1910 - 9,578 1920 - 9,220 1930 - 8,951 1940 - 7,130 1950 - 7,189 1960 - 5,081 1970 - 4,357 1980 - 4,292 1990 - 3,810 2000 - 3,786
As of the census of 2000, there were 3,786 people, 1,597 households, and 1,049 families residing in the county. The population density was 7 people per square mile (3/km²). There were 2,327 housing units at an average density of 4 per square mile (2/km²). The racial makeup of the county was 98.86% White, 0.13% Black or African American, 0.11% Native American, 0.08% Asian, 0.03% Pacific Islander, 0.16% from other races, and 0.63% from two or more races. 0.77% of the population were Hispanic or Latino of any race.
There were 1,597 households out of which 25.70% had children under the age of 18 living with them, 59.00% were married couples living together, 4.30% had a female householder with no husband present, and 34.30% were non-families. 30.80% of all households were made up of individuals and 16.70% had someone living alone who was 65 years of age or older. The average household size was 2.34 and the average family size was 2.93.
In the county the population was spread out with 24.20% under the age of 18, 5.00% from 18 to 24, 21.60% from 25 to 44, 26.20% from 45 to 64, and 23.00% who were 65 years of age or older. The median age was 44 years. For every 100 females there were 98.00 males. For every 100 females age 18 and over, there were 96.80 males.
The median income for a household in the county was $30,679, and the median income for a family was $36,875. Males had a median income of $27,580 versus $18,411 for females. The per capita income for the county was $15,618. About 7.00% of families and 10.10% of the population were below the poverty line, including 14.40% of those under age 18 and 9.10% of those age 65 or over.