As of the census of 2000, there were 24,525 people, 9,185 households, and 6,888 families residing in the county. The population density was 57 people per square mile. There were 11,046 housing units at an average density of 26 per square mile. The racial makeup of the county was 95.89% White, 1.94% Black or African American, 0.45% Native American, 0.24% Asian, 0.02% Pacific Islander, 0.44% from other races, and 1.02% from two or more races. Approximately 1.28% of the population were Hispanic or Latino of any race. Among the major ancestries reported in Warren County were 41.4% German, 13.8% American, 10.2% Irish and 7.0% English ancestry. There were 9,185 households out of which 34.70% had children under the age of 18 living with them, 62.20% were married couples living together, 8.90% had a female householder with no husband present, and 25.00% were non-families. 20.80% of all households were made up of individuals and 8.80% had someone living alone who was 65 years of age or older. The average household size was 2.64 and the average family size was 3.05. In the county, the population was spread out with 26.90% under the age of 18, 7.60% from 18 to 24, 28.80% from 25 to 44, 23.70% from 45 to 64, and 13.00% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 98.60 males. For every 100 females age 18 and over, there were 96.10 males. The median income for a household in the county was $41,016, and the median income for a family was $46,863. Males had a median income of $36,315 versus $23,443 for females. The per capita income for the county was $19,690. About 6.40% of families and 8.60% of the population were below the poverty line, including 10.50% of those under age 18 and 10.40% of those age 65 or over.
Politics
Local
All of the elected positions in the county are held by Republicans.
Warren County is a part of Missouri's 10th District in the Missouri Senate and is currently represented by . The 10th Senatorial District consists of all of Audrain, Callaway, Lincoln, Monroe, Montgomery, and Warren counties.
At the presidential level, like many exurban counties, Warren County tends to lean Republican. Bill Clinton in 1992 is the solitary Democratic presidential nominee to carry Warren County since Stephen Douglas in 1860, and Clinton only won with 37.1 percent of the vote. Like most rural and exurban areas throughout Northeast Missouri, voters in Warren County generally adhere to socially and culturally conservative principles which tend to influence their Republican leanings. The initiative narrowly passed the state with 51 percent of support from voters as Missouri became one of the first states in the nation to approve embryonic stem cell research. Despite Warren County's longstanding tradition of supporting socially conservative platforms, voters in the county have a penchant for advancing populist causes like increasing the minimum wage. In 2006, Missourians voted on a proposition to increase the minimum wage in the state to $6.50 an hour—it passed Warren County with 77.48 percent of the vote. The proposition strongly passed every single county in Missouri with 78.99 percent voting in favor.
Missouri presidential preference primary (2008)
Former U.S. Senator Hillary Rodham Clinton received more votes, a total of 1,971, than any candidate from either party in Warren County during the 2008 presidential primary.
