Coordinates: 38°57′06″N 92°19′43″W / 38.951561°N 92.328638°W / 38.951561; -92.328638 (Boone County, Missouri)
According to the U.S. Census Bureau, the county has a total area of 691 square miles (1,790 km), of which 685 square miles (1,770 km) is land and 5.6 square miles (15 km) (0.8%) is water. The Missouri River makes up the southern border of the county.
As of the census of 2000, there were 135,454 people, 53,094 households, and 31,378 families residing in the county. The population density was 198 people per square mile (76/km²). There were 56,678 housing units at an average density of 83 per square mile (32/km²). The racial makeup of the county was 85.43% White, 8.54% Black or African American, 0.42% Native American, 2.96% Asian, 0.03% Pacific Islander, 0.69% from other races, and 1.93% from two or more races. Approximately 1.78% of the population were Hispanic or Latino of any race. 24.6% claimed German, 12.3% American, 11.2% English and 9.8% Irish ancestry.
There were 53,094 households out of which 30.30% had children under the age of 18 living with them, 45.50% were married couples living together, 10.40% had a female householder with no husband present, and 40.90% were non-families. 28.70% of all households were made up of individuals and 6.20% had someone living alone who was 65 years of age or older. The average household size was 2.38 and the average family size was 2.97.
In the county, the population was spread out with 22.80% under the age of 18, 19.90% from 18 to 24, 29.90% from 25 to 44, 18.80% from 45 to 64, and 8.60% who were 65 years of age or older. The median age was 30 years. For every 100 females, there were 93.50 males. For every 100 females age 18 and over, there were 90.90 males.
The median income for a household in the county was $37,485, and the median income for a family was $51,210. Males had a median income of $33,304 versus $25,990 for females. The per capita income for the county was $19,844. About 7.60% of families and 14.50% of the population were below the poverty line, including 12.10% of those under age 18 and 5.90% of those age 65 or over.
There are 121,319 registered voters.