Black Jack is a second-ring suburb of St. Louis, located in northern St. Louis County, Missouri, United States. The population was 6,929 at the 2010 census.
A post office called Black Jack was established in 1872, and remained in operation until 1906. The community was named for a grove of blackjack oak trees near the original town site.
Black Jack is located at 38°47′27″N 90°15′43″W (38.790799, −90.261885).
According to the United States Census Bureau, the city has a total area of 2.60 square miles (6.73 km2), of which 2.59 square miles (6.71 km2) is land and 0.01 square miles (0.03 km2) is water.
As of the census of 2010, there were 6,929 people, 2,591 households, and 1,797 families living in the city. The population density was 2,675.3 inhabitants per square mile (1,032.9/km2). There were 2,809 housing units at an average density of 1,084.6 per square mile (418.8/km2). The racial makeup of the city was 16.3% White, 81.2% African American, 0.1% Native American, 0.4% Asian, 0.2% from other races, and 1.8% from two or more races. Hispanic or Latino of any race were 0.7% of the population.
There were 2,591 households of which 35.5% had children under the age of 18 living with them, 42.6% were married couples living together, 21.4% had a female householder with no husband present, 5.3% had a male householder with no wife present, and 30.6% were non-families.