636

The 636 area code is a vital part of Missouri's telephone system, especially around the St. Louis area. Geographical Coverage: Area code 636 primarily serves the east-central part of Missouri. This includes mainly the western suburbs of St. Louis, encompassing parts of Chesterfield and Fenton in St. Louis County, as well as all of Washington, Union, De Soto, Troy, St. Charles, Jefferson, and Warren counties​​​​​​. Establishment and Service Areas: This area code was assigned on April 15th, 1999, and officially went into service on May 22nd, 1999. It was created following a split from area code 314. The 636 area code also includes various ZIP Codes such as 63146, 63044, 63043, among others​​​​​​. Largest City and Time Zone: The largest city served by the 636 area code is O'Fallon, Missouri. The area is located in the Central Standard Time (CST) zone and observes Daylight Saving Time​​. In conclusion, area code 636 plays a significant role in Missouri's telecommunication infrastructure, connecting various key regions and serving numerous communities in and around St. Louis. Its establishment in 1999 marked an important evolution in the state's numbering plan, accommodating the growing demand for telephone numbers in the region.