As of 2000, the population was 21,912. Its county seat is Maryville.
It is the largest area wise 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 four national championship football games, two 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, Missouri 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 at the Northwest 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.
As of the census of 2000, there were 21,912 people, 8,138 households, and 4,817 families residing in the county. The population density was 25 people per square mile (10/km²). There were 8,909 housing units at an average density of 10 per square mile (4/km²). The racial makeup of the county was 96.58% White, 1.35% Black or African American, 0.23% Native American, 0.87% Asian, 0.02% Pacific Islander, 0.21% from other races, and 0.74% from two or more races. 0.71% of the population were Hispanic or Latino of any race.
There were 8,138 households out of which 27.30% had children under the age of 18 living with them, 50.00% were married couples living together, 6.20% had a female householder with no husband present, and 40.80% were non-families. 30.00% of all households were made up of individuals and 11.60% had someone living alone who was 65 years of age or older. The average household size was 2.33 and the average family size was 2.94.
In the county the population was spread out with 19.40% under the age of 18, 25.10% from 18 to 24, 23.10% from 25 to 44, 18.60% from 45 to 64, and 13.80% who were 65 years of age or older. The median age was 30 years. For every 100 females there were 99.70 males. For every 100 females age 18 and over, there were 97.00 males.
The median income for a household in the county was $31,781, and the median income for a family was $42,203. Males had a median income of $28,388 versus $21,267 for females. The per capita income for the county was $15,384. About 8.30% of families and 16.50% of the population were below the poverty line, including 11.20% of those under age 18 and 13.30% of those age 65 or over.
Nodaway County is served by Northwest Missouri Regional Airport in Maryville which is a general aviation airport with no commercial service.
Maryville also has one cab that can be located in the yellow pages, as well as a nightly bus from Maryville to Kansas City.