Lewis County is a county located in the northeastern portion of the U.S. state of Missouri. As of the 2010 census, the population was 10,211. Its county seat is Monticello. The county was organized January 2, 1833 and named for Meriwether Lewis, the explorer and Governor of the Louisiana Territory.
According to the U.S. Census Bureau, the county has a total area of 511 square miles (1,320 km), of which 505 square miles (1,310 km) is land and 5.8 square miles (15 km) (1.1%) is water.
As of the census of 2010, there were 10,211 people, 3,956 households, and 2,709 families residing in the county. The population density was 21 people per square mile. The racial makeup of the county was 95.92% White, 2.53% Black or African American, 0.16% Native American, 0.20% Asian, 0.02% Pacific Islander, 0.44% from other races, and 0.73% from two or more races. Approximately 0.73% of the population were Hispanic or Latino of any race. 34.9% were of German, 18.3% American, 11.2% English and 10.8% Irish ancestry.
The average household size was 2.46 and the average family size was 3.00. In the county, the population was spread out with 25.00% under the age of 18, 12.90% from 18 to 24, 24.60% from 25 to 44, 21.40% from 45 to 64, and 16.10% who are 65 years of age or older and 51% of female population. The median age is 36 years.
Median income for a household in the county is $30,651, and the median income for a family was $35,740. Males had a median income of $27,778 versus $19,679 for females. The per capita income for the county was $14,746. 16.10% of the population and 10.70% of families were below the poverty line.