Missouri · Central Time
636 Area Code
Area code 636 is in Missouri, serving outer St. Louis suburbs: St. Charles, Jefferson and Franklin counties and west St. Louis County. It is in the Central Time zone.
Last updated October 1, 2026 · Source: NANPA
Where is the 636 area code?
636 is a Missouri area code covering outer St. Louis suburbs: St. Charles, Jefferson and Franklin counties and west St. Louis County. In the wider directory it sits in the Midwest region.
Cities in the 636 area code
- O'Fallon
- St. Charles
- St. Peters
- Wentzville
- Chesterfield
- Ballwin
- Wildwood
- Arnold
- Lake St. Louis
- Festus
- Washington
- Eureka
- Troy
Counties served by 636
St. Charles County, Jefferson County, Franklin County, Lincoln County, Warren County and St. Louis County.
Dialing 636
O'Fallon, MO is currently served by the single area code 636, with no overlay. Ten-digit dialing (area code + seven-digit number) always works and is increasingly the norm nationwide; some local calls may still connect with seven digits. If a future overlay is added, 10-digit dialing would become mandatory.
From outside the US, dial +1 636 followed by the seven-digit number.
History of the 636 area code
636 went into service on May 22, 1999, created when it was split from 314. It serves O'Fallon and the surrounding part of Missouri. For how codes are created, split, and overlaid, see how area codes work.
Is 636 a scam or spam risk?
636 is a legitimate geographic area code, not a premium or toll line, so a call from it costs you nothing extra. That said, scammers frequently spoof real local area codes to look familiar on caller ID. A genuine 636 number on your screen is no guarantee the caller is in O'Fallon, MO or trustworthy. See spam & scam-risk area codes for how spoofing works and how to respond.
Other Missouri area codes
Explore more
See every code in Missouri, compare codes across the Midwest region, or view all Central Time codes. You can also browse the 6XX block or the complete numeric list of US area codes.
New to how this all works? Start with how area codes work, then read up on overlays, 10-digit dialing, and spam & scam-risk codes. To check another number, use the area code lookup tool.
Quick answers
636 area code FAQ
Where is the 636 area code?
The 636 area code is in Missouri, covering outer St. Louis suburbs: St. Charles, Jefferson and Franklin counties and west St. Louis County, in the Midwest region.
What cities are in the 636 area code?
Cities in the 636 area code include O'Fallon, St. Charles, St. Peters, Wentzville, Chesterfield, Ballwin, Wildwood, Arnold, Lake St. Louis and Festus.
What time zone is 636 in?
636 is in the Central Time zone.
When did the 636 area code start?
636 went into service on May 22, 1999.
Do I have to dial 10 digits for 636?
Ten-digit dialing always works, and many areas now require it; some local calls in this area may still connect with seven digits.
Is 636 a toll-free or premium code?
No. 636 is a standard geographic area code, so calling it costs the same as any local or long-distance call on your plan. Toll-free calls use 800, 888, 877, 866, 855, 844 or 833.