Area code 636 is a telephone area code in North American Numbering Plan (NANP) for the east-central part of the U.S. state of Missouri, comprising mainly the western suburbs of St. Louis.

The first three digits of a phone number in the United States are known as the area code. The area code is used to identify a geographic region. You can use an online area code lookup tool or a phone book to find out which state or county a particular area code belongs to.

Area codes 314 and 557 are telephone area codes in the North American Numbering Plan (NANP) in the U.S. state of Missouri, serving the city of St. Louis and most of its inner-ring suburbs in neighboring St. Louis County. The numbering plan area is bordered to the west by area code 636, which serves St.