High Quality Content by WIKIPEDIA articles! Atchison is a city situated along the Missouri River in the eastern part of Atchison County, located in northeast Kansas, in the Central United States. As of the 2010 census, the city population was 11,021. It is the county seat and most populous city of Atchison County. The city is named in honor of David Rice Atchison, United States senator from Missouri, and was the original eastern terminus of the Atchison, Topeka, and Santa Fe Railroad.