| ZIP Codes: | 6 ZIP Codes (6 Standard, 0 PO Box, 0 Unique) [See All] |
| Area Codes: | 217 / 447 |
| Timezone: | Central (GMT -06:00) |
| Local Time: | 2:11:59 PM |
| Population: | 15,671 [See All] |
| FIPS: | 17023 |
| Land Area: | 557 sq mi |
| Water Area: | 3 sq mi |
| Coordinates: | 39.3556, -87.7879 |
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15,671 residents live across 6 ZIPs covering 557 sq mi, served by 6 distinct USPS-recognized cities.
Population moved from 16,909 to 15,671 from 2014 to 2024 — a -7.3% change. 1 ZIPs gained residents, 5 lost.
The county's wealthiest ZIP 62477 (West Union, $88,646 median) and poorest ZIP 62423 (Dennison, $47,179) are 16.3 miles apart — a 1.9× income gap across local geography.
Median home values vary 2.0× across this county — from $87,200 in 62442 (Martinsville) to $173,300 in 62423 (Dennison).
Density varies 5× across the county — from 8 people/sq mi in 62477 (West Union) to 40 in 62441 (Marshall).
Educational attainment ranges from 17.2% bachelor's+ in 62474 (Westfield) to 29.5% in 62441 (Marshall) — the breadth of educational profiles across the area.
Within Illinois, this is the #67 most populous of 102 counties and ranks #56 for median household income .
Weighted by population, the typical household earns about $73,401 across the county — reflecting what a typical resident sees, not a simple ZIP average.
24.5% of adults age 25+ hold a bachelor's degree or higher (2,722 of 11,124 reporting).
6 Standard delivery, 0 PO Box only, 0 single-entity Unique ZIPs serve this county.
A frontier county — vast land area with only a few residents per square mile. Daily life looks very different here than in the country's denser counties.
Clark County lost 7.3% of residents between 2014 and 2024. ZIPs that shed the largest share:
| ZIP | City | Type | Population | Median Income | Area (sq mi) | 10-yr Growth |
|---|---|---|---|---|---|---|
| 62441 | Marshall | Standard | 7,003 | $80,738 | 173.9 | -5.6% |
| 62420 | Casey | Standard | 4,299 | $65,771 | 126.0 | -5.5% |
| 62442 | Martinsville | Standard | 2,671 | $70,284 | 134.7 | 19.5% |
| 62474 | Westfield | Standard | 626 | $67,083 | 33.3 | -36.4% |
| 62423 | Dennison | Standard | 546 | $47,179 | 24.2 | -20.4% |
| 62477 | West Union | Standard | 526 | $88,646 | 64.5 | -49.1% |