It was named after General Joseph Warren, a hero in the American Revolutionary War.

[4] The present Warren County Court House was opened in 1939.

[14] At the 2000 census there were 40,671 people, 14,708 households, and 11,207 families in the county.

There were 15,289 housing units at an average density of 27 per square mile (10/km2).

The racial makeup of the county was 98.08% White, 0.27% Black or African American, 0.17% Native American, 0.38% Asian, 0.04% Pacific Islander, 0.29% from other races, and 0.76% from two or more races.

Of the 14,708 households 37.80% had children under the age of 18 living with them, 64.50% were married couples living together, 8.80% had a female householder with no husband present, and 23.80% were non-families.