[2] The county was formed in 1855, and was named for General Lewis Cass, an American military officer, politician, and statesman.

[3][4][5] Cass County is included in the Omaha–Council Bluffs, NE–IA Metropolitan Statistical Area.

[6] In the Nebraska license plate system, Cass County is represented by the prefix 20 (it had the 20th-largest number of vehicles registered in the county when the license plate system was established in 1922).

The racial makeup of the county was 89.3% White, 0.7% Black or Black or African American, 1.0% Native American, 0.6% Asian, 0.1% Native Hawaiian and Pacific Islander, 0.6% other races, and 1.5% from two or more races.

As of the 2000 United States Census,[13] there were 24,334 people, 9,161 households, and 6,806 families in the county.

21.60% of all households were made up of individuals, and 9.40% had someone living alone who was 65 years of age or older.

Cass County is divided into the following divisions, called precincts, except for the cities of Plattsmouth and Weeping Water.

At the presidential level, Cass County voters have voted predominantly for the Republican candidate.