Atchison County, Missouri

Atchison County
Location within the U.S. state of Missouri
Missouri's location within the U.S.
Coordinates: 40°26′N 95°26′W / 40.43°N 95.43°W / 40.43; -95.43
Country United States
State Missouri
FoundedFebruary 14, 1845
Named afterDavid Rice Atchison
SeatRock Port
Largest cityTarkio
Area
  Total
550 sq mi (1,400 km2)
  Land547 sq mi (1,420 km2)
  Water2.8 sq mi (7 km2)  0.5%
Population
 (2020)
  Total
5,305
  Density9.6/sq mi (3.7/km2)
Time zoneUTC−6 (Central)
  Summer (DST)UTC−5 (CDT)
Congressional district6th
Websitewww.atchisoncounty.org

Atchison County is the northwesternmost county in the U.S. state of Missouri. As of the 2020 census, the county had a population of 5,305. Its county seat is Rock Port. It was originally known as Allen County when it was detached from Holt County in 1843. The county was officially organized on February 14, 1845, and named for U.S. Senator David Rice Atchison from Missouri.