Area code 636 serves the western suburbs of St. Louis, Missouri, including cities like St. Charles, O'Fallon, Chesterfield, and Washington. It was created in 1999 from a split of area code 314 to address the rapid suburban expansion outside the St. Louis city limits. The region is home to a mix of residential communities, business parks, and historical attractions. With easy access to downtown St. Louis, 636 has become a popular area for commuters and families. Ten-digit dialing is required, and the code is frequently used in regional business and real estate branding. 636 represents one of Missouri’s most economically active suburban zones.