West Alton is a city in St. Charles County, Missouri, United States. The population was 522 at the 2010 census. It is located at the tip of the peninsula formed by the confluence of the Missouri and Mississippi Rivers.
A post office called West Alton has been in operation since 1895. The community was named from its location on the western bank of the Mississippi River opposite Alton, Illinois.
West Alton is located at 38°52′4″N 90°13′33″W (38.867798, -90.225856), in St Charles County.
According to the United States Census Bureau, the city has a total area of 37.06 square miles (95.98 km2), of which 28.81 square miles (74.62 km2) is land and 8.25 square miles (21.37 km2) is water. West Alton is located at the intersection of U.S. Route 67 and County Highway 94.
As of the census of 2010, there were 522 people, 203 households, and 144 families living in the city. The population density was 18.1 inhabitants per square mile (7.0/km2).