[6] In the Nebraska license plate system, Clay County is represented by the prefix 30 (it had the 30th-largest number of vehicles registered in the county when the license plate system was established in 1922).

[7] As of the 2000 United States Census,[29] there were 7,039 people, 2,756 households, and 1,981 families in the county.

49.4% were of German, 7.2% English, 7.2% American, 5.4% Swedish and 5.3% Irish ancestry.

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.

In only one national election since 1936 has the county selected the Democratic Party candidate.