| Zip Code (Post Office) | Population 2000 | Population Est. 2004 | Pop. Projections 2009 | Pop. Proj. 2004-9 - % Change | |||
| 63301 Saint Charles | 46,059 | 46,356 | 52,300 | 12.82 | |||
| 63303 Saint Charles | 41,575 | 45,934 | 50,549 | 10.05 | |||
| 63304 Saint Charles | 38,586 | 43,604 | 49,582 | 13.71 | |||
| 63332 Augusta | 1,207 | 935 | 1072 | 14.65 | |||
| 63341 Defiance | 3,143 | 4,101 | 4,517 | 10.14 | |||
| 63348 Foristell | 4,526 | 4,647 | 5,294 | 13.92 | |||
| 63366 O' Fallon | 57,473 | 69,108 | 78,498 | 13.59 | |||
| 63367 Lake Saint Louis | 8,350 | 11,661 | 12,614 | 8.17 | |||
| 63373 Portage Des Sioux | 680 | 468 | 540 | 15.38 | |||
| 63376 Saint Peters | 68,741 | 72,061 | 80,239 | 11.35 | |||
| 63385 Wentzville | 13,825 | 17,257 | 19,894 | 15.28 | |||
| 63386 West Alton | 557 | 551 | 652 | 18.32 | |||
| Sources: Census 2000 | |||||||
| GeoLytics: CensusCD, Est. 2004, Projctions (2009) | |||||||