Weather & Climate in Illiopolis, IL
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Illiopolis experiences four distinct seasons with an average annual temperature of 53°F (12°C). Winters average 27°F in January while summers reach 76°F in July. Annual precipitation totals 38.6 inches. The area receives 18.7 inches of snow annually, a moderate snowfall amount. The city sits at an elevation of 595 feet.
Temperature
27°F Jan (-3°C)
76°F Jul (24°C)
| Annual Average | 53.1°F |
| 2% below US avg | |
| January Average | 27°F (-3°C) |
| July Average | 76°F (24°C) |
Geography
| Elevation | 595 ft (181 m) |
| Area | 0.2 sq mi (0.5 km²) |
| Population Density | 1,256/sq mi |
| Coordinates | 39.8498°N, 89.2521°W |
| Timezone | America/Chicago |
| County | Christian County County |
| Nearest Airport | Central Il Regional/Bloomington-Normal (BMI) 47 miles away |
Precipitation & Snow
Air Quality
Natural Hazard Risk
| Overall Risk | Relatively Low |
| Risk Score | 54.0 / 100 |
| Social Vulnerability | 17.1 / 100 |
| Community Resilience | 85.0 / 100 |
Hazard Breakdown
| Tornado | Relatively Low |
| Hurricane | Very Low |
| Earthquake | Relatively Low |
| Wildfire | Very Low |
| Flood | Relatively Low |
| Hail | Relatively Low |
| Strong Wind | Relatively Moderate |
| Heat Wave | Relatively Low |
| Winter Weather | Relatively Low |
| Lightning | Relatively Low |
| Ice Storm | Relatively Low |
| Drought | Relatively High |
| Cold Wave | Relatively Moderate |
| Landslide | Very Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Earthquake History
7 earthquakes (M2.5+) recorded within 150 km since 1990. Strongest on record: M3.4.
| Mar 2, 1990 | 9 km NW of Vernon, Illinois | M3.4 | 111 km | 0 km |
| May 13, 2025 | 7 km SSW of Lerna, Illinois | M3.3 | 96 km | 10 km |
| Jan 29, 1993 | 7 km WNW of Brownstown, Illinois | M3.2 | 93 km | 5 km |
| Jul 1, 2017 | 9 km SSE of Mulberry Grove, Illinois | M3.1 | 111 km | 17 km |
| Sep 5, 2004 | 3 km WNW of Saint Peter, Illinois | M2.9 | 112 km | 33 km |
| Apr 24, 1990 | 5 km SW of Newton, Illinois | M2.9 | 134 km | 18 km |
| Mar 28, 2024 | 1 km NNE of Germantown, Illinois | M2.8 | 144 km | 24 km |
Source: USGS Earthquake Catalog (M2.5+, 1990-2025). Sorted by magnitude.
Tornado History
779 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF4. Total: 28 fatalities, 819 injuries.
| Date | Rating | Distance | Path | Fatalities |
| Nov 17, 2013 | EF4 | 90 km | 46.4 mi | 3 |
| May 5, 1977 | EF4 | 45 km | 7.3 mi | 0 |
| Mar 20, 1976 | EF4 | 39 km | 63.7 mi | 0 |
| Jun 14, 1957 | EF4 | 40 km | 4.3 mi | 2 |
| Dec 1, 2018 | EF3 | 50 km | 12.5 mi | 0 |
| Nov 17, 2013 | EF3 | 79 km | 18.7 mi | 0 |
| Apr 19, 2011 | EF3 | 67 km | 4.3 mi | 0 |
| Dec 31, 2010 | EF3 | 54 km | 3.6 mi | 0 |
| Aug 19, 2009 | EF3 | 29 km | 24.3 mi | 0 |
| May 10, 2003 | EF3 | 78 km | 17.5 mi | 0 |
| Jun 1, 1999 | EF3 | 69 km | 10.0 mi | 1 |
| Apr 19, 1996 | EF3 | 89 km | 4.0 mi | 0 |
| Apr 19, 1996 | EF3 | 53 km | 9.4 mi | 0 |
| Apr 19, 1996 | EF3 | 7 km | 14.5 mi | 0 |
| May 13, 1995 | EF3 | 86 km | 25.0 mi | 0 |
| May 9, 1995 | EF3 | 41 km | 50.0 mi | 0 |
| Jul 26, 1978 | EF3 | 45 km | 8.9 mi | 0 |
| Aug 21, 1977 | EF3 | 70 km | 26.9 mi | 6 |
| Aug 6, 1977 | EF3 | 47 km | 4.1 mi | 0 |
| Mar 20, 1976 | EF3 | 60 km | 8.8 mi | 0 |
Source: NOAA Storm Prediction Center (EF0+, 1950-2024, US only).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 27°F (-3°C) | 2.1 in | Coldest |
| February | 32°F (-0°C) | 2.0 in | Driest |
| March | 42°F (6°C) | 2.5 in | |
| April | 53°F (12°C) | 3.7 in | |
| May | 64°F (18°C) | 5.0 in | Wettest |
| June | 73°F (23°C) | 4.3 in | |
| July | 76°F (24°C) | 4.4 in | Warmest |
| August | 74°F (23°C) | 3.1 in | |
| September | 67°F (19°C) | 3.2 in | |
| October | 55°F (13°C) | 3.4 in | |
| November | 43°F (6°C) | 2.9 in | |
| December | 32°F (0°C) | 2.1 in |
Illiopolis has a seasonal temperature swing of 48°F / from 27°F in January to 76°F in July. Total annual precipitation is 38.6 inches, with May being the wettest month (5.0") and February the driest (2.0").