Clinton County 411 square miles land area has a population of 40,543 people, 15,416 households, and 11,068 families. The population density is 38/km˛ (99/mi˛). There are 16,577 housing units at an average density of 16/km˛ (40/mi˛). The racial makeup of the county is 95.99% White, 2.19% Black or African American, 0.26% Native American, 0.38% Asian, 0.00% Pacific Islander, 0.20% from other races, and 0.97% from two or more races. 0.66% of the population is Hispanic or Latino of any race. The median income for a household in the county is $40,467, and the median income for a family is $48,158.

There are thirteen townships in Clinton County: Adams, Chester, Clark, Green, Jefferson, Liberty, Marion, Richland, Union, Vernon, Washington, Wayne, Wilson. Its County seat is Wilmington.

Neighboring areas include: Greene County, Fayette County, Highland County, Brown County, Clermont County, and Warren County.