Mehlville is an unincorporated community and census-designated place (CDP) in south St. Louis County, Missouri, United States, an area locally known as "South County".

At the 2000 census there were 28,822 people, 12,541 households, and 7,775 families living in the CDP.

There were 12,982 housing units at an average density of 1,762.8 per square mile (680.6/km2).

The racial makeup of the CDP was 97.08% White, 0.75% African American, 0.13% Native American, 1.77% Asian, 0.02% Pacific Islander, 0.34% from other races, and 0.61% from two or more races.

The Mehlville School District has approximately 12,000 students currently enrolled.