Atchison County was named for David H. Atchison, a U.S. Senator from Missouri, and President of the United States Senate at the date of the passage of the Act for the organization of the Territory of Kansas. He was a Pro-Slavery Democrat, and zealous partisan leader in the discussions and movements affecting the interests of slavery and its attempted establishment in the new state to be created. Atchison County, whose county seat is Atchison was organized in 1855.