Pettis County is a county located in the U.S. state of Missouri. The county was organized in 1833 and is named for U.S. Congressman Spencer Darwin Pettis. As of 2000, the population was 39,403. Its county seat is Sedalia.
There were 15,568 households out of which 32.50% had children under the age of 18 living with them, 53.30% were married couples living together, 10.50% had a female householder with no husband present, and 32.10% were non-families. 27.00% of all households were made up of individuals and 11.70% had someone living alone who was 65 years of age or older. The average household size was 2.49 and the average family size was 3.01.
In the county the population was spread out with 26.30% under the age of 18, 9.30% from 18 to 24, 27.90% from 25 to 44, 21.10% from 45 to 64, and 15.40% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 94.40 males. For every 100 females age 18 and over, there were 91.70 males.
The median income for a household in the county was $31,822, and the median income for a family was $38,073. Males had a median income of $29,221 versus $19,554 for females. The per capita income for the county was $16,251. About 10.20% of families and 12.80% of the population were below the poverty line, including 16.60% of those under age 18 and 10.50% of those age 65 or over.