Founded in 1812, Saint Charles County is one of 114 counties in the state of Missouri. Historically, Saint Charles County was one of the five original counties. The city of Saint Charles is the county seat. With FIPS code of 183, Saint Charles County has a population of 409,981 and area of 561 square miles (1,453 km2).
List of all cities in Saint Charles County, MO alphabetically
| City/Town | Postal Code | Area Code |
| Augusta, MO | 63332 | 636 |
| Black Walnut, MO | 63301 | 636 |
| Cottleville, MO | 63304 | 636 |
| 63338 | 636 | |
| 63366 | 636 | |
| 63376 | 636 | |
| Dardenne, MO | 63366 | 636 |
| 63368 | 636 | |
| Dardenne Prairie, MO | 63366 | 636 |
| 63368 | 636 | |
| Defiance, MO | 63341 | 636 |
| Femme Osage, MO | 63332 | 636 |
| Flinthill, MO | 63346 | 636 |
| Foristell, MO | 63348 | 636 |
| Gilmore, MO | 63385 | 636 |
| Harvester, MO | 63303 | 636 |
| Josephville, MO | 63385 | 636 |
| Kampville, MO | 63301 | 636 |
| Kampville Beach, MO | 63301 | 636 |
| Kampville Court, MO | 63301 | 636 |
| Lake Saint Louis, MO | 63367 | 636 |
| Machens, MO | 63373 | 636 |
| Matson, MO | 63341 | 636 |
| New Melle, MO | 63365 | 636 |
| O Fallon, MO | 63366 | 636 |
| 63367 | 636 | |
| 63368 | 636 | |
| Orchard Farm, MO | 63301 | 636 |
| Portage des Sioux, MO | 63373 | 636 |
| Saint Charles, MO | 63301 | 636 |
| 63302 | 636 | |
| 63303 | 636 | |
| 63304 | 636 | |
| 63366 | 636 | |
| Saint Paul, MO | 63366 | 636 |
| Saint Peters, MO | 63303 | 636 |
| 63304 | 636 | |
| 63366 | 636 | |
| 63368 | 636 | |
| 63376 | 636 | |
| Schluersburg, MO | 63332 | 636 |
| South Shore, MO | 63301 | 636 |
| Weldon Spring, MO | 63304 | 636 |
| Weldon Spring Heights, MO | 63304 | 636 |
| Wentzville, MO | 63385 | 636 |
| West Alton, MO | 63386 | 636 |