Pettis County is a county located in west central U.S. state of Missouri. As of the 2020 census, the population was 42,980. Its county seat is Sedalia. The county was organized on January 24, 1833, and named after former U.S. Representative Spencer Darwin Pettis.

Sedalia is a city located approximately 30 miles south of the Missouri River and, as the county seat of Pettis County, Missouri, United States, it is the principal city of the Sedalia Micropolitan Statistical Area. As of the 2020 census, the city had a total population of 21,725. Sedalia is also the location of the Missouri State Fair and the Scott Joplin Ragtime Festival. U.S. Routes 50 and 65 intersect in the city.