| ZIP Codes: | 8 ZIP Codes (7 Standard, 1 PO Box, 0 Unique) [See All] |
| Area Codes: | 319 / 563 |
| Timezone: | Central (GMT -06:00) |
| Local Time: | 11:53:08 PM |
| Population: | 25,857 [See All] |
| FIPS: | 19017 |
| CBSA: | Waterloo-Cedar Falls, IA |
| Land Area: | 485 sq mi |
| Water Area: | 4 sq mi |
| Coordinates: | 42.7703, -92.3408 |
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25,857 residents live across 8 ZIPs covering 485 sq mi, served by 8 distinct USPS-recognized cities.
Population moved from 25,304 to 25,632 from 2014 to 2024 — a +1.3% change. 3 ZIPs gained residents, 4 lost.
The county's wealthiest ZIP 50647 (Janesville, $104,063 median) and poorest ZIP 50631 (Frederika, $58,750) are 18.1 miles apart — a 1.8× income gap across local geography.
Median home values vary 3.2× across this county — from $98,800 in 50631 (Frederika) to $314,200 in 50647 (Janesville).
Density varies 34× across the county — from 16 people/sq mi in 50666 (Plainfield) to 532 in 50631 (Frederika).
Educational attainment ranges from 7.8% bachelor's+ in 50666 (Plainfield) to 46.4% in 50622 (Denver) — the breadth of educational profiles across the area.
Within Iowa, this is the #23 most populous of 99 counties and ranks #19 for median household income .
Weighted by population, the typical household earns about $86,359 across the county — reflecting what a typical resident sees, not a simple ZIP average.
35.6% of adults age 25+ hold a bachelor's degree or higher (6,086 of 17,112 reporting).
7 Standard delivery, 1 PO Box only, 0 single-entity Unique ZIPs serve this county.
| ZIP | City | Type | Population | Median Income | Area (sq mi) | 10-yr Growth |
|---|---|---|---|---|---|---|
| 50677 | Waverly | Standard | 12,673 | $85,633 | 128.9 | 6.3% |
| 50622 | Denver | Standard | 3,549 | $95,089 | 26.7 | 7.4% |
| 50674 | Sumner | Standard | 3,446 | $72,794 | 157.4 | -0.1% |
| 50676 | Tripoli | Standard | 2,017 | $87,115 | 56.4 | -14.0% |
| 50647 | Janesville | Standard | 1,978 | $104,063 | 31.3 | 8.0% |
| 50668 | Readlyn | Standard | 1,216 | $85,956 | 35.6 | -7.8% |
| 50666 | Plainfield | Standard | 753 | $79,867 | 47.7 | -33.4% |
| 50631 | Frederika | PO Box | 225 | $58,750 | 0.4 | — |