| ZIP Codes: | 24 ZIP Codes (19 Standard, 5 PO Box, 0 Unique) [See All] |
| Area Codes: | 779 / 815 |
| Timezone: | Central (GMT -06:00) |
| Local Time: | 11:53:19 PM |
| Population: | 104,357 [See All] |
| FIPS: | 17099 |
| CBSA: | Ottawa, IL |
| Land Area: | 1,251 sq mi |
| Water Area: | 13 sq mi |
| Coordinates: | 41.3275, -88.9224 |
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104,357 residents live across 24 ZIPs covering 1,251 sq mi, served by 24 distinct USPS-recognized cities.
Population moved from 108,481 to 104,274 from 2014 to 2024 — a -3.9% change. 9 ZIPs gained residents, 14 lost.
The county's wealthiest ZIP 61373 (Utica, $109,000 median) and poorest ZIP 61364 (Streator, $59,060) are 22.4 miles apart — a 1.8× income gap across local geography.
Median home values vary 2.9× across this county — from $103,700 in 61364 (Streator) to $305,500 in 60549 (Serena).
Density varies 13× across the county — from 20 people/sq mi in 61334 (Lostant) to 249 in 61354 (Peru).
Educational attainment ranges from 13.4% bachelor's+ in 61364 (Streator) to 26.2% in 60531 (Leland) — the breadth of educational profiles across the area.
Within Illinois, this is the #19 most populous of 102 counties and ranks #23 for median household income .
Weighted by population, the typical household earns about $73,295 across the county — reflecting what a typical resident sees, not a simple ZIP average.
19.8% of adults age 25+ hold a bachelor's degree or higher (14,609 of 73,863 reporting).
19 Standard delivery, 5 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.
| ZIP | City | Type | Population | Median Income | Area (sq mi) | 10-yr Growth |
|---|---|---|---|---|---|---|
| 61350 | Ottawa | Standard | 23,713 | $77,921 | 155.7 | -1.5% |
| 61364 | Streator | Standard | 17,963 | $59,060 | 154.0 | -11.4% |
| 61301 | La Salle | Standard | 10,398 | $60,328 | 43.5 | -1.6% |
| 61354 | Peru | Standard | 10,290 | $76,392 | 41.3 | -4.7% |
| 61342 | Mendota | Standard | 8,543 | $65,348 | 111.8 | -6.3% |
| 61341 | Marseilles | Standard | 7,692 | $72,530 | 98.4 | 1.2% |
| 60551 | Sheridan | Standard | 5,058 | $86,786 | 62.2 | 5.5% |
| 61348 | Oglesby | Standard | 4,375 | $76,369 | 40.2 | -4.4% |
| 61360 | Seneca | Standard | 3,610 | $95,093 | 49.2 | -7.5% |
| 60518 | Earlville | Standard | 3,289 | $69,980 | 128.4 | -12.4% |
| 61373 | Utica | Standard | 2,123 | $109,000 | 46.2 | 14.8% |
| 60531 | Leland | Standard | 1,885 | $79,808 | 62.8 | 10.4% |
| 61370 | Tonica | Standard | 1,215 | $91,094 | 51.6 | -7.1% |
| 61325 | Grand Ridge | Standard | 949 | $87,500 | 48.1 | 2.6% |
| 60549 | Serena | Standard | 784 | $108,417 | 23.7 | -16.1% |
| 61334 | Lostant | Standard | 738 | $86,250 | 37.7 | 31.1% |
| 61358 | Rutland | Standard | 407 | $88,393 | 27.2 | -5.8% |
| 60470 | Ransom | Standard | 358 | $85,000 | 39.9 | -38.3% |
| 61372 | Troy Grove | PO Box | 300 | $83,917 | 0.5 | 112.8% |
| 61316 | Cedar Point | PO Box | 256 | $74,375 | 0.7 | -14.7% |
| 61321 | Dana | Standard | 224 | $80,257 | 26.7 | 15.5% |
| 61332 | Leonore | PO Box | 104 | $50,313 | 0.1 | 35.1% |
| 61371 | Triumph | PO Box | 83 | — | 0.1 | — |
| 60557 | Wedron | PO Box | 0 | — | 0.6 | -100.0% |