Greenup County is a part of the Huntington-Ashland, WV-KY-OH, Metropolitan Statistical Area (MSA). As of the 2000 census, the MSA had a population of 288,649.
As of the census of 2000, there were 36,891 people, 14,536 households, and 11,032 families residing in the county. The population density was 107 per square mile (41 /km). There were 15,977 housing units at an average density of 46 per square mile (18 /km). The racial makeup of the county was 98.07% White, 0.57% Black or African American, 0.19% Native American, 0.38% Asian, 0.15% from other races, and 0.64% from two or more races. 0.55% of the population were Hispanic or Latino of any race.
There were 14,536 households out of which 32.00% had children under the age of 18 living with them, 62.30% were married couples living together, 10.40% had a female householder with no husband present, and 24.10% were non-families. 21.70% of all households were made up of individuals and 10.00% had someone living alone who was 65 years of age or older. The average household size was 2.51 and the average family size was 2.91.
In the county the population was spread out with 23.60% under the age of 18, 7.90% from 18 to 24, 27.90% from 25 to 44, 26.00% from 45 to 64, and 14.60% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 92.80 males. For every 100 females age 18 and over, there were 89.30 males.
The median income for a household in the county was $32,142, and the median income for a family was $38,928. Males had a median income of $35,475 versus $21,198 for females. The per capita income for the county was $17,137. About 11.60% of families and 14.10% of the population were below the poverty line, including 18.60% of those under age 18 and 9.90% of those age 65 or over.