Clay County is part of the Hastings micropolitan area.
In the Nebraska license plate system, Clay County is represented by the prefix 30 (it had the thirtieth-largest number of vehicles registered in the county when the license plate system was established in 1922).
1860 - 165 1870 - 54 1880 - 11,294 1890 - 16,310 1900 - 15,735 1910 - 15,729 1920 - 14,486 1930 - 13,571 1940 - 10,445 1950 - 8,700 1960 - 8,717 1970 - 8,266 1980 - 8,106 1990 - 7,213 2000 - 7,039
As of the census of 2000, there were 7,039 people, 2,756 households, and 1,981 families residing in the county. The population density was 12 people per square mile (5/km²). There were 3,066 housing units at an average density of 5 per square mile (2/km²). The racial makeup of the county was 97.57% White, 0.17% Black or African American, 0.31% Native American, 0.30% Asian, 1.24% from other races, and 0.41% from two or more races. 3.48% of the population were Hispanic or Latino of any race. 49.4% were of German, 7.2% English, 7.2% American, 5.4% Swedish and 5.3% Irish ancestry according to Census 2000.
There were 2,756 households out of which 32.90% had children under the age of 18 living with them, 63.70% were married couples living together, 5.50% had a female householder with no husband present, and 28.10% were non-families. 25.70% of all households were made up of individuals and 13.10% 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 3.03.
In the county the population was spread out with 27.30% under the age of 18, 5.90% from 18 to 24, 25.30% from 25 to 44, 23.60% from 45 to 64, and 18.00% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 95.10 males. For every 100 females age 18 and over, there were 95.00 males.
The median income for a household in the county was $34,259, and the median income for a family was $39,541. Males had a median income of $28,321 versus $19,870 for females. The per capita income for the county was $16,870. About 8.50% of families and 10.40% of the population were below the poverty line, including 13.40% of those under age 18 and 6.60% of those age 65 or over.