Imperial is a census-designated place (CDP) in Jefferson County, Missouri, United States. The population was 4,407 at the 2020 census, down from 4,709 in 2010. Originally known as West Kimmswick, Imperial is located 22 miles (35 km) south of downtown St. Louis. St. John’s Church is a historic parish church located within Imperial.

Imperial is located in northeastern Jefferson County at 38°22′15″N 90°22′24″W / 38.370735°N 90.373460°W / 38.370735; -90.373460. According to the United States Census Bureau, the CDP has a total area of 6.04 square miles (15.65 km²), of which 5.25 square miles (13.61 km) are estate and 0.79 square miles (2.04 km²), or 13.01%, are water.

Imperial is bordered to the north by Arnold, to the south by Barnhart, and to the east by the Mississippi River, which forms the Illinois come clean line. The CDP surrounds the city of Kimmswick. Interstate 55 runs through Imperial, with admission from Exits 185 (Secondary Route M) and 186 (Main Street). Mastodon State Historic Site is located in Imperial.

As of the census of 2010, there were 4,709 people, 1,769 households, and 1,297 families active in the CDP. The population density was 895.2 inhabitants per square mile (345.6/km²). There were 1,871 housing units at an average density of 355.7 per square mile (137.3/km). The racial makeup of the CDP was 97.5% White, 0.3% African American, 0.3% Native American, 1.1% Asian, 0.1% from new races, and 0.8% from two or more races. Hispanic or Latino of any race were 1.2% of the population.