West Alton is a city in St. Charles County, Missouri, United States. The population was 359 at the 2020 census. It is located at the tip of the peninsula formed by the confluence of the Missouri and Mississippi Rivers and is directly across Alton, Illinois.

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.