St. Peters is a city in St. Charles County, Missouri, United States. The population was 57,732 at the 2020 census, making it the eleventh-largest city in Missouri. It is a northwestern suburb of St. Louis.

St. Charles County is in the central eastern part of the U.S. state of Missouri. As of the 2020 census, the population was 405,262, making it Missouri's third-most populous county. Its county seat is St. Charles. The county was organized October 1, 1812, and named for Saint Charles Borromeo, an Italian cardinal.