Festus is a city in Jefferson County, Missouri, United States. It had a population of 11,602 individuals as of the 2010 census. Festus and its particular neighbor Crystal City are often collectively known as the "Twin Cities".
Festus is located at 38°13′10″N 90°24′3″W (38.219490, -90.400936).
According to the United States Census Bureau, the city has a total area of 5.71 square miles (14.79 km2), all land.
Festus was first called Tanglefoot, and under the latter name was platted in 1878. A post office called Festus has been in operation since 1883.
At the 2010 census there were 11,602 people, 4,636 households, and 3,036 families living in the city. The population density was 2,031.9 inhabitants per square mile (784.5/km2). There were 4,972 housing units at an average density of 870.8 per square mile (336.2/km2). The racial makeup of the city was 93.5% White, 3.4% African American, 0.2% Native American, 0.8% Asian, 0.2% from other races, and 1.9% from two or more races. Hispanic or Latino of any race were 1.2%.
Of the 4,636 households 37.0% had children under the age of 18 living with them, 46.2% were married couples living together, 14.5% had a female householder with no husband present, 4.8% had a male householder with no wife present, and 34.5% were non-families. 28.7% of households were one person and 12.1% were one person aged 65 or older. The average household size was 2.47 and the average family size was 3.04.