Jefferson County weather, town by town
10 places in Jefferson County, Illinois, each with its own live forecast and radar, and where a station sits close enough, measured weather records.
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Measured at the NOAA stations serving these towns, daily records 1895 to 2026. Station extremes, not official state records.
Jefferson County Weather Facts
Jefferson County has 10 places on myweatherrock (7 villages, 2 cities, 1 census-designated places), each with its own live forecast, hourly timeline, ten day outlook and radar. The hottest day in the station records is 114°F at Mt Vernon 3 Ne on July 14, 1936. The coldest night is -22°F at Mt Vernon 3 Ne on February 10, 1899. The wettest day brought 9.1 inches of rain at Rend Lake Dam on November 14, 1993. The biggest single-day snow measured 12.28 inches at Waltonville on December 6, 2013. Those are station measurements from NOAA's daily records, 1895 to 2026, not official state records. By area the largest place is Mount Vernon, about 15 square miles.
About Jefferson County weather
The map on the Now tab shows every Jefferson County town's current temperature from our own server, one dot per town. Tap any dot, or type a town above, for that town's full forecast.
What the weather is usually like
Across the 10 Jefferson County towns with station normals, the warmest month is July, when the day usually reaches 86°F, and the coldest is January, when the night usually falls to 22°F. May is the wettest, with rain on about 13 days.
Means of the 1991 to 2020 station normals serving these towns, as published by NOAA; each town's page carries its own.
Where these numbers come from
- Current conditions and forecast: NOAA forecast grids decoded on our own server, corrected against the nearest reporting station and our own radar. Open-Meteo is consulted only as a fallback when our server is silent.
- Records: computed by myweatherrock from NOAA GHCN-Daily station records at the stations serving these towns. Measurements, not estimates.
- Warnings and alerts: the National Weather Service, passed through unchanged.
Jefferson County weather records
Measured at the NOAA stations serving these towns, daily records 1895 to 2026. Station extremes, not official state records.
Common questions about Jefferson County weather
- What is the hottest temperature recorded at a Jefferson County station?
- 114°F at Mt Vernon 3 Ne on July 14, 1936, in the NOAA daily station records myweatherrock holds (1895 to 2026).
- What is the coldest temperature recorded at a Jefferson County station?
- -22°F at Mt Vernon 3 Ne on February 10, 1899.
- What is the most rain a Jefferson County station has measured in one day?
- 9.1 inches at Rend Lake Dam on November 14, 1993.
- What is the biggest one-day snowfall at a Jefferson County station?
- 12.28 inches at Waltonville on December 6, 2013.
- How many Jefferson County towns have a weather page here?
- 10: 7 villages, 2 cities, 1 census-designated places. Each page carries current conditions, the hourly timeline, the ten day outlook, radar, and where a station sits close enough, measured records.
- Where does the Jefferson County forecast come from?
- NOAA forecast grids (the National Weather Service digital forecast, the National Blend of Models, HRRR and GFS) decoded on our own server, corrected against the nearest reporting station and our own radar. Open-Meteo is consulted only as a fallback when our server is silent.
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