As of 2010, the population was 23,370. Its county seat is Maryville. It is the largest in area of the counties added to Missouri in the 1836 Platte Purchase, and the fourth largest county in the state of Missouri.
It has a rich agricultural history, including the home of trainers Ben Jones and Jimmy Jones whose horses won six Kentucky Derby races and two Triple Crowns.
The grounds of Northwest Missouri State University make up the official Missouri State Arboretum and were a re-creation of the landscape of the 1904 St. Louis World's Fair. ESPN has carried appearances of the university in five national championship football games, three of which they won.
Supreme Court Justice Clarence Thomas gave up his quest to become a priest while attending Conception Seminary College which also includes a minor basilica. The Benedictine Sisters of Perpetual Adoration convent in neighboring Clyde has 550 relics of saints-the largest collection in the U.S.
Located in Tornado Alley, there have been numerous tornadoes to hit the county, including an F4 tornado on April 10, 1979, that obliterated the town of Braddyville, Iowa just across the county line. Tornadoes have struck two of the county's biggest buildings-the Administration Building on the campus of Northwest Missouri State University and Conception Abbey. The 1881 Hopkins tornado is believed to have been one of the first recorded F5 tornados.
Some sensational murders have drawn attention to the county including a profile by CBS 60 Minutes, as well as movies.
Life in the county was chronicled by native Homer Croy in a series of books, articles, films and Broadway shows in the 1920s and 1930s.