Andrew County, organized 1841, is one of six counties in the Indian Platte Purchase Territory annexed to Missouri in 1837. Named for Andrew Jackson Davis, a St. Louis editor, the county was first settled in the middle 1830s. Pioneers were from Ohio, Indiana, Tennessee, Kentucky, Virginia, and other parts of Missouri.

DeKalb County was organized on 25 February 1845 from Clinton County and is named after the American Revolutionary War general Johann de Kalb. Many records were lost in an 1878 courthouse fire.

Organized January 26, 1833, from Cooper and Saline Counties, and named for Spencer Pettis, a Missouri congressman. Sedalia is the county seat and also home of the annual Missouri State Fair. Pettis is a strong rural county, but Sedalia was closely tied to the railroad lines passing through it. Those times are almost forgotten, except for the annual Ragtime Festival held to commemorate the partnership in Sedalia of music publisher John Stark and ragtime composer Scott Joplin.

Saline County was organized November 25, 1820, (effective January 1, 1821) from Cooper County and named for its numerous salt springs. Bordered on the north by the Missouri River, Saline County was considered to be part of "Little Dixie" in the antebellum years.