Crystal City is a city in Jefferson County, Missouri, United States. The population was 4,855 at the 2010 census. It was 4,247 at the 2000 census.
Crystal City and its neighbor Festus are often collectively known as the "Twin Cities".
Crystal City was originally called New Detroit. A post office called Crystal City has been in operation since 1872. In the 1860s, Pittsburgh Plate Glass Company opened a glass manufacturing plant, which is the origin of the city's name. Currently, the PPG plant property remains empty and undeveloped. It was purchased by Wings Enterprises in the mid 2000s with the intentions of constructing an Iron Ore smelter on the property. In the early 2000s, the state of Missouri forced Doe Run Company to purchase 160 homes in Herculaneum after it was found over 56% of children within a quarter mile of the plant had high levels of lead in their blood.