Question: Atchison is a city and county seat of which county?

Context paragraphs:
Mason, Michigan: Mason is a city in the U.S. state of Michigan.  It is named after the state's first governor, Stevens T. Mason.  As of the 2010 census, the city population was 8,252.  It is the county seat of Ingham County.  Mason is the only city in the U.S. that serves as a county seat ahead of a state capital, with the capital of Lansing also in Ingham County.  Despite Mason being the county seat, many county offices and courtrooms are located in Lansing.

Atchison County, Missouri: Atchison County is the northwestern-most county in the U.S. state of Missouri.  As of the 2010 census, the county had a population of 5,685.  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.

Ellicott City, Maryland: Ellicott City is an unincorporated community and census-designated place, along with being the county seat of local government in Howard County, Maryland, United States.  It is part of the Baltimore Metropolitan Area.  The population was 65,834 at the 2010 census.  Founded in 1772, the town contains the B. & O. Railroad Museum's branch at the Ellicott City Station, built in 1830 as the first terminus of the initial line.  The downtown historic district is located in the valley of the small Tiber River, with its east end abutting the Patapsco River, which forms the Baltimore County line.  As of the 2000 census, Ellicott City surpassed Towson (county seat of neighboring Baltimore County) for the first time, as the largest unincorporated county seat in the country.

Coronado, Kansas: Coronado is an unincorporated community in Wichita County, Kansas, United States, was once a thriving community.  Platted in 1885, Coronado was involved in the bloodiest county seat fight in the history of the American West.  The shoot-out on February 27, 1887, with boosters—some would say hired gunmen—from nearby Leoti left several people dead and wounded.  Afterwards numerous famous lawmen from Dodge City, which included Wyatt Earp and Bat Masterson, gathered to calm the storm that ensued after the bloody fight.  A small town called Farmer City, which was located between Coronado and Leoti, was hoped by some to become the county seat—which would end the fighting.  Leoti later won the right to become the county seat and now the other two towns consist mainly of farmland.

Van Buren, Missouri: Van Buren is a city that is the county seat of Carter County, Missouri, in the United States.  It is the largest town in Carter County.  Van Buren was founded in 1833 as the county seat of Ripley County and was named after then Vice President of the United States, Martin Van Buren.  In 1859 Van Buren became a part of the newly created Carter County and was subsequently selected to be the county seat.  The 2010 U.S. Census shows Van Buren with a population of 819, a decrease of 3.1 percent from its 2000 population of 845.

Atchison County, Kansas: Atchison County (county code AT) is a county located in northeastern Kansas, in the Central United States.  As of the 2010 census, the county population was 16,924.  Its county seat and most populous city is Atchison.  The county is named in honor of David Rice Atchison, a United States Senator from Missouri.

Atchison, Kansas: Atchison is a city and county seat of Atchison County, Kansas, United States, and situated along the Missouri River.  As of the 2010 census, its population was 11,021.  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 Railway.  Atchison was the birthplace of aviator Amelia Earhart, and the Amelia Earhart Festival is held annually in July.  Atchison is also home of Benedictine College, a Catholic liberal-arts college.

Rock Port, Missouri: Rock Port is a city in, and the county seat of, Atchison County, Missouri, United States.  The population was 1,318 at the 2010 census.

Johnston Library: The Johnston Library is a historic library located at 210 W. 10th St. in Baxter Springs, Kansas.  The building was constructed in 1872 to serve as a courthouse during Baxter Springs' unsuccessful attempt to become the Cherokee County seat.  Though Baxter Springs had lost an election to choose the county seat in 1869 to Columbus, supporters of both cities had attempted to fraudulently swing the election in their favor, and Baxter Springs hoped it could still become county seat in the future.  The building initially served as the county jail and sheriff's office until Columbus completed its jail in 1880.  After this, Baxter Springs ultimately gave up its attempts to become the county seat, and the building became its city hall.  In 1905, resident Niles P. Johnston bequeathed $5,000 to the city to start a library, and the city hall building was chosen to house it.

Cerro Gordo County Courthouse (Iowa): The Cerro Gordo County Courthouse is located in Mason City, Iowa, United States.  When Cerro Gordo County was created in 1855 and Mason City was selected to be the county seat.  Dissatisfaction in the western part of the county led the Iowa legislature to appoint three new commissioners who would move the county seat to Livonia.  A courthouse was built there.  A petition signed by over half of the citizens of the county requested that the county seat be moved back to Mason City.  Mason City also won the election in 1858 to decide the matter 155-48.  Two courthouses have stood in Mason City prior to the present Modernist structure that was occupied by the county in 1960.  It had been built as the Standard Oil Building, and was acquired by the county in 1959 for $159,400 and then remodeled for their use.

Supporting paragraphs: Atchison, Kansas Atchison County, Kansas
Answer: Atchison County, Kansas