[3][4][5] It was named after Richard Mentor Johnson, who was Vice President of the United States from 1837 to 1841.

[6] In the Nebraska license plate system, Johnson County is represented by the prefix 57 (it had the fifty-seventh-largest number of vehicles registered in the county when the license plate system was established in 1922).

The terrain of Johnson County consists of low rolling hills whose flattened tops are mostly used for agriculture.

The Big Nemaha River flows southeastward through the central part of the county.

As of the 2000 United States Census,[14] there were 4,488 people, 1,887 households, and 1,254 families in the county.

In no national election since 1964 has the county selected a Democratic Party candidate (as of 2024).