According to the 2000 U.S. Census, the county has a total area of 418.85 square miles (1,084.8 km2), of which 416.52 square miles (1,078.8 km2) (or 99.44%) is land and 2.33 square miles (6.0 km2) (or 0.56%) is water.
There were 5,259 households out of which 35.30% had children under the age of 18 living with them, 58.00% were married couples living together, 8.60% had a female householder with no husband present, and 29.10% were non-families. 25.60% of all households were made up of individuals and 13.00% had someone living alone who was 65 years of age or older. The average household size was 2.56 and the average family size was 3.07.
In the county the population was spread out with 25.90% under the age of 18, 8.20% from 18 to 24, 31.10% from 25 to 44, 20.90% from 45 to 64, and 13.90% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 113.30 males. For every 100 females age 18 and over, there were 116.80 males.
The median income for a household in the county was $37,168, and the median income for a family was $42,487. Males had a median income of $26,807 versus $20,853 for females. The per capita income for the county was $16,609. About 7.30% of families and 9.90% of the population were below the poverty line, including 13.10% of those under age 18 and 9.00% of those age 65 or over.
^Laura King Van Dusen, "Benjamin Ratcliff: Park County Pioneer, Civil War Veteran, Triple Murderer; What Happened and Why", Historic Tales from Park County: Parked in the Past (Charleston, South Carolina: The History Press, 2013), ISBN 978-1-62619-161-7, pp. 127-134.
History of Cole, Moniteau, Morgan, Benton, Miller, Maries and Osage counties, Missouri : from the earliest time to the present, including a department devoted to the preservation of sundry personal, business,professional and the private records; besides a valuable fund of notes, original observations, etc. etc. (1889) online