According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. The county is located in the Pennyroyal Plateau region of the state.
As of the census of 2000, there were 16,405 people, 6,415 households, and 4,638 families residing in the county. The population density was. There were 7,016 housing units at an average density of. The racial makeup of the county was 87.84% White, 10.22% Black or African American, 0.17% Native American, 0.55% Asian, 0.06% Pacific Islander, 0.30% from other races, and 0.87% from two or more races. 0.91% of the population were Hispanics or Latinos of any race. There were 6,415 households out of which 33.80% had children under the age of 18 living with them, 56.80% were married couplesliving together, 11.50% had a female householder with no husband present, and 27.70% were non-families. 24.20% of all households were made up of individuals and 10.40% had someone living alone who was 65 years of age or older. The average household size was 2.52 and the average family size was 2.97. The age distribution was 26.20% under the age of 18, 8.50% from 18 to 24, 29.20% from 25 to 44, 23.00% from 45 to 64, and 13.10% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 95.30 males. For every 100 females age 18 and over, there were 91.60 males. The median income for a household in the county was $36,432, and the median income for a family was $42,525. Males had a median income of $32,160 versus $22,667 for females. The per capita income for the county was $17,150. About 8.50% of families and 11.60% of the population were below the poverty line, including 14.00% of those under age 18 and 15.90% of those age 65 or over.
In contrast to the Western Coalfield and the eastern part of the Pennyroyal Plateau, Simpson County was not highly pro-Union during the Civil War. Consequently, Simpson was as reliably Democratic as the Jackson Purchase and Bluegrass during the following century: no Republican carried Simpson County until Richard Nixon’s 1972 landslide. As with all of rural Kentucky, the social liberalism of the Democratic Party – rejected by many southern whites – has led to an increase in registered Republicans, and many people registered as Democrats vote for Republican candidates, especially at the national level. In 2014, of a population of 17,800, there were 12,700 registered voters in Simpson County: 8,040 were Democrats, 3,587 were Republican, and 1073 were unaffiliated or registered with another party.
