| ZIP Codes: | 17 ZIP Codes (13 Standard, 4 PO Box, 0 Unique) [See All] |
| Area Codes: | 314 / 557 / 636 |
| Timezone: | Central (GMT -06:00) |
| Local Time: | 2:12:45 PM |
| Population: | 416,486 [See All] |
| FIPS: | 29183 |
| CBSA: | St. Louis, MO-IL |
| Land Area: | 599 sq mi |
| Water Area: | 32 sq mi |
| Coordinates: | 38.7766, -90.6768 |
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416,486 residents live across 17 ZIPs covering 599 sq mi, served by 13 distinct USPS-recognized cities.
Population moved from 371,402 to 416,435 from 2014 to 2024 — a +12.1% change. 10 ZIPs gained residents, 3 lost.
The county's wealthiest ZIP 63341 (Defiance, $170,598 median) and poorest ZIP 63301 (Saint Charles, $85,308) are 21.4 miles apart — a 2.0× income gap across local geography.
Median home values vary 2.3× across this county — from $267,600 in 63301 (Saint Charles) to $606,800 in 63341 (Defiance).
Density varies 110× across the county — from 27 people/sq mi in 63332 (Augusta) to 2,903 in 63303 (Saint Charles).
Educational attainment ranges from 32.7% bachelor's+ in 63332 (Augusta) to 54.1% in 63341 (Defiance) — the breadth of educational profiles across the area.
Within Missouri, this is the #3 most populous of 116 counties and ranks #1 for median household income with the #9 fastest decade growth .
Weighted by population, the typical household earns about $107,064 across the county — reflecting what a typical resident sees, not a simple ZIP average.
42.6% of adults age 25+ hold a bachelor's degree or higher (123,222 of 289,063 reporting).
13 Standard delivery, 4 PO Box only, 0 single-entity Unique ZIPs serve this county.
| ZIP | City | Type | Population | Median Income | Area (sq mi) | 10-yr Growth |
|---|---|---|---|---|---|---|
| 63376 | Saint Peters | Standard | 74,962 | $96,393 | 33.9 | 3.4% |
| 63366 | O Fallon | Standard | 54,769 | $100,621 | 68.3 | 13.5% |
| 63301 | Saint Charles | Standard | 52,667 | $85,308 | 105.4 | 6.0% |
| 63385 | Wentzville | Standard | 51,330 | $112,199 | 70.2 | 39.6% |
| 63368 | O Fallon | Standard | 46,966 | $124,297 | 16.9 | 7.1% |
| 63303 | Saint Charles | Standard | 46,089 | $99,138 | 15.9 | -1.4% |
| 63304 | Saint Charles | Standard | 43,195 | $114,442 | 43.1 | 8.4% |
| 63367 | Lake Saint Louis | Standard | 29,725 | $137,648 | 13.6 | 40.3% |
| 63348 | Foristell | Standard | 10,394 | $115,661 | 55.0 | 56.3% |
| 63341 | Defiance | Standard | 3,515 | $170,598 | 56.1 | -0.2% |
| 63332 | Augusta | Standard | 1,651 | $146,146 | 62.3 | 21.3% |
| 63373 | Portage Des Sioux | Standard | 690 | $88,750 | 19.1 | 51.3% |
| 63386 | West Alton | Standard | 482 | $110,250 | 39.2 | -19.8% |
| 63365 | New Melle | PO Box | 51 | $53,542 | 0.0 | — |
| 63338 | Cottleville | PO Box | — | — | 0.0 | — |
| 63302 | Saint Charles | PO Box | — | — | 0.0 | — |
| 63346 | Flinthill | PO Box | — | — | 0.0 | — |