Barnhart is a census-designated place (CDP) in Jefferson County, Missouri, United States. The population was 5,682 at the 2010 census.
Barnhart is located at 38°20′16″N 90°24′14″W (38.337914, -90.403822).
According to the United States Census Bureau, the CDP has a total area of 5.25 square miles (13.60 km2), of which 5.09 square miles (13.18 km2) is land and 0.16 square miles (0.41 km2) is water.
As of the census of 2010, there were 5,682 people, 1,920 households, and 1,576 families living in the CDP. The population density was 1,116.3 inhabitants per square mile (431.0/km2). There were 2,003 housing units at an average density of 393.5 per square mile (151.9/km2). The racial makeup of the CDP was 97.4% White, 0.5% African American, 0.3% Native American, 0.4% Asian, 0.3% from other races, and 1.1% from two or more races. Hispanic or Latino of any race were 2.1% of the population.
There were 1,920 households, of which 44.0% had children under the age of 18 living with them, 65.3% were married couples living together, 10.8% had a female householder with no husband present, 6.0% had a male householder with no wife present, and 17.9% were non-families. 12.6% of all households were made up of individuals, and 2.7% had someone living alone who was 65 years of age or older. The average household size was 2.93 and the average family size was 3.17.
The median age in the CDP was 34.5 years.