In 1947, when the American Telephone and Telegraph Company (AT&T) published the first configuration of a nationwide telephone numbering plan, the first version of the North American Numbering Plan (NANP), the U.S. state of Missouri was divided into two numbering plan areas (314 and 816). In 1950, the boundaries were redrawn in the creation of a third numbering plan area, 816. This configuration was stable for forty years into the 1990s, when rapid expansion of telecommunication service required additional area codes.
| Area code | Created | Parent NPA | Overlay | Numbering plan area |
|---|---|---|---|---|
| 314 | 1947 | – | 314/557 | St. Louis and many of its immediate suburbs |
| 557 | 2022 | 314 | ||
| 573 | 1996 | 314 | 235/573 | Eastern and southeastern Missouri (Columbia, Jefferson City, Rolla, Cape Girardeau, Perryville, and Hannibal) |
| 235 | 2024 | 573 | ||
| 636 | 1999 | 314 | – | St. Charles, Jefferson, and western St. Louis counties, which forms a ring around the immediate St. Louis area |
| 816 | 1947 | – | 816/975 | Kansas City and St. Joseph metropolitan areas |
| 975 | 2002 | 816 | ||
| 417 | 1950 | 816, 314 | – | Southwestern part of Missouri (Springfield, Joplin, and Branson) |
| 660 | 1997 | 816 | – | Northern and western Missouri (St. Joseph metropolitan areas, but including Sedalia, Kirksville, Warrensburg, Maryville) |
