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Weather & Climate in Oswego, IL
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Oswego experiences four distinct seasons with an average annual temperature of 50°F (10°C). Winters average 23°F in January while summers reach 74°F in July. The area gets 275 sunny days per year, well above the U.S. average of 205 / making it one of the sunnier locations in the country. Annual precipitation totals 39.5 inches. The area receives 27.9 inches of snow annually, a moderate snowfall amount. Air quality is rated Good with a median AQI of 43. The city sits at an elevation of 659 feet.
Temperature
23°F Jan (-5°C)
74°F Jul (24°C)
| Annual Average | 50.2°F |
| 7% below US avg | |
| January Average | 23°F (-5°C) |
| July Average | 74°F (24°C) |
| Sunny Days | 275 days/yr |
Geography
| Elevation | 659 ft (201 m) |
| Area | 15.0 sq mi (39.0 km²) |
| Population Density | 2,240/sq mi |
| Coordinates | 41.6832°N, 88.3388°W |
| Timezone | America/Chicago |
| County | Kendall County County |
| Nearest Airport | Joliet Regional (JOT) 14 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 43.0 |
| Rating | Good |
Natural Hazard Risk
| Overall Risk | Relatively Low |
| Risk Score | 80.3 / 100 |
| Social Vulnerability | 10.6 / 100 |
| Community Resilience | 96.0 / 100 |
Hazard Breakdown
| Tornado | Relatively Moderate |
| Hurricane | Very Low |
| Earthquake | Relatively Low |
| Wildfire | Very Low |
| Flood | Relatively Moderate |
| Hail | Very Low |
| Strong Wind | Relatively High |
| Heat Wave | Relatively Low |
| Winter Weather | Relatively Low |
| Lightning | Relatively Low |
| Ice Storm | Relatively Low |
| Drought | Relatively Low |
| Cold Wave | Relatively High |
| Landslide | Very Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Earthquake History
8 earthquakes (M2.5+) recorded within 150 km since 1990. Strongest on record: M4.2.
| Jun 28, 2004 | 12 km NW of Dayton, Illinois | M4.2 | 53 km | 10 km |
| Feb 10, 2010 | 2 km NW of Lily Lake, Illinois | M3.8 | 34 km | 10 km |
| Sep 2, 1999 | 8 km W of Amboy, Illinois | M3.5 | 91 km | 5 km |
| Nov 4, 2013 | 1 km SSW of Lyons, Illinois | M3.2 | 45 km | 1 km |
| Jul 15, 2024 | 2 km WNW of Somonauk, Illinois | M3.1 | 31 km | 10 km |
| Mar 25, 2015 | 3 km WNW of Lake in the Hills, Illinois | M2.9 | 56 km | 6 km |
| Jun 10, 2013 | 4 km NNE of Virgil, Illinois | M2.6 | 37 km | 5 km |
| Mar 15, 2025 | 6 km W of Dwight, Illinois | M2.6 | 68 km | 5 km |
Source: USGS Earthquake Catalog (M2.5+, 1990–2025). Sorted by magnitude.
Tornado History
629 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF5. Total: 122 fatalities, 2,279 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Aug 28, 1990 | EF5 | 1 km | 16.4 mi | 29 |
| Apr 9, 2015 | EF4 | 81 km | 30.1 mi | 2 |
| Jun 29, 1979 | EF4 | 20 km | 5.4 mi | 0 |
| Jun 13, 1976 | EF4 | 28 km | 3.3 mi | 2 |
| Sep 28, 1972 | EF4 | 77 km | 5.2 mi | 0 |
| Apr 21, 1967 | EF4 | 42 km | 15.0 mi | 33 |
| Apr 21, 1967 | EF4 | 52 km | 8.8 mi | 1 |
| Apr 21, 1967 | EF4 | 77 km | 25.5 mi | 24 |
| Apr 11, 1965 | EF4 | 60 km | 9.1 mi | 6 |
| Apr 17, 1963 | EF4 | 59 km | 57.3 mi | 1 |
| Jun 20, 2021 | EF3 | 14 km | 17.6 mi | 0 |
| Feb 28, 2017 | EF3 | 65 km | 11.5 mi | 2 |
| Jun 22, 2015 | EF3 | 42 km | 16.3 mi | 0 |
| Jun 5, 2010 | EF3 | 73 km | 8.6 mi | 0 |
| Jun 5, 2010 | EF3 | 85 km | 7.8 mi | 0 |
| Jan 7, 2008 | EF3 | 96 km | 10.8 mi | 0 |
| Jan 7, 2008 | EF3 | 88 km | 13.2 mi | 0 |
| Apr 20, 2004 | EF3 | 92 km | 15.8 mi | 8 |
| Mar 27, 1991 | EF3 | 23 km | 15.0 mi | 0 |
| Apr 27, 1984 | EF3 | 15 km | 9.0 mi | 1 |
Source: NOAA Storm Prediction Center (EF0+, 1950–2024, US only).
Tsunami History
1 tsunami recorded within 500 km. Highest wave on record: 3.0 m (10 ft).
| Year | Location | Cause | Max Wave | Deaths | Distance |
| 1954 | MICHIGAN CITY, IN (LAKE MICHIGAN) | Avalanche | 3.0 m | 7 | 121 km |
Source: NOAA/NCEI Historical Tsunami Database.
Wildfire History
11 wildfires (100+ acres) recorded within 100 km. Largest: UNNAMED (1,741 acres, 2019).
| Year | Name | Acres Burned | Distance |
| 2019 | UNNAMED | 1,741 | 37 km |
| 2019 | UNNAMED | 1,664 | 40 km |
| 2021 | NORTHEAST PRAIRIE UNIT 3 | 978 | 44 km |
| 2024 | NORTHEAST PRAIRIE 3 RX | 938 | 42 km |
| 1986 | OGDEN DUNS | 863 | 94 km |
| 2021 | UNNAMED | 738 | 41 km |
| 2021 | MIDDLE GRANT CREEK | 700 | 38 km |
| 2019 | UNNAMED | 698 | 41 km |
| 2024 | IBSP SOUTH F1 RX | 690 | 91 km |
| 2021 | 21-INDU TOLLESTON DUNES EAST | 594 | 94 km |
| 2017 | UNNAMED | 549 | 38 km |
Source: NIFC/IRWIN Wildfire Records (100+ acres).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 23°F (-5°C) | 1.5 in | Coldest |
| February | 26°F (-3°C) | 1.3 in | Driest |
| March | 37°F (3°C) | 2.6 in | |
| April | 49°F (9°C) | 3.8 in | |
| May | 60°F (16°C) | 3.9 in | |
| June | 70°F (21°C) | 4.2 in | Wettest |
| July | 74°F (24°C) | 3.9 in | Warmest |
| August | 71°F (22°C) | 4.0 in | |
| September | 64°F (18°C) | 3.8 in | |
| October | 52°F (11°C) | 2.7 in | |
| November | 39°F (4°C) | 3.0 in | |
| December | 26°F (-3°C) | 2.3 in |
Oswego has a seasonal temperature swing of 51°F / from 23°F in January to 74°F in July. Total annual precipitation is 37.1 inches, with June being the wettest month (4.2") and February the driest (1.3").