[2] The county is named in honor of Charles Carroll of Carrollton, signer of the Declaration of Independence.

It was named after Charles Carroll[3] of Carrollton, Maryland, the only Roman Catholic and longest-living signer of the Declaration of Independence.

In 1855, the county government was established in Carrollton and in 1858, the first courthouse was built.

In 1869, the seat was moved to Carroll City (today Carroll) which was centrally located and connected to the Chicago and North Western Transportation Company.

91.28% were non-Hispanic White, 1.26% were Black, 2.86% were Hispanic, 0.15% were Native American, 0.36% were Asian, 0.00% were Native Hawaiian or Pacific Islander and 4.08% were some other race or more than one race.

[11] As of the census[12] of 2000, there were 21,421 people, 8,486 households, and 5,668 families residing in the county.

29.60% of all households were made up of individuals, and 15.50% had someone living alone who was 65 years of age or older.