According to the 2000 U.S. Census, the county has a total area of 599.94 square miles (1,553.8 km2), of which 592.26 square miles (1,533.9 km2) (or 98.72%) is land and 7.69 square miles (19.9 km2) (or 1.28%) is water.
There were 9,284 households out of which 32.60% had children under the age of 18 living with them, 56.00% were married couples living together, 9.20% had a female householder with no husband present, and 30.60% were non-families. 26.10% of all households were made up of individuals and 11.90% had someone living alone who was 65 years of age or older. The average household size was 2.50 and the average family size was 3.00.
In the county the population was spread out with 26.30% under the age of 18, 8.40% from 18 to 24, 27.40% from 25 to 44, 22.70% from 45 to 64, and 15.30% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 97.30 males. For every 100 females age 18 and over, there were 93.70 males.
The median income for a household in the county was $30,977, and the median income for a family was $36,770. Males had a median income of $26,225 versus $18,903 for females. The per capita income for the county was $15,144. About 10.80% of families and 14.20% of the population were below the poverty line, including 19.30% of those under age 18 and 14.70% of those age 65 or over.
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