Monticello weather by month
What a typical year looks like in Monticello, Illinois: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at Champaign 9 SW, 17 km from Monticello; records cover 2002–2026.
The year at a glance
- Precipitation a year
- 39.6 in1006 mm
- Snow a year
- Rare
- Last spring freeze
- Apr 20
- First fall freeze
- Oct 12
- Heating degree days
- 5,858
- Cooling degree days
- 821
Freeze dates are medians (half of years earlier, half later). Degree days use a 65°F base; HVAC design temperatures here are −5°−20° (heating, 99%) and 92°33° (cooling, 1%).
Month by month
Monticello in January
Highs average 33°1° and lows 17°−8°, with 2.3 in59 mm of precipitation in a typical January.
- Record high
- 67°19° (2008)
- Record low
- −18°−28° (2003)
- Heating degree days
- 1232
- Cooling degree days
- 0
Monticello in February
Highs average 38°3° and lows 21°−6°, with 2 in51 mm of precipitation in a typical February.
- Record high
- 75°24° (2024)
- Record low
- −19°−28° (2015)
- Heating degree days
- 994
- Cooling degree days
- 0
Monticello in March
Highs average 50°10° and lows 30°−1°, with 2.9 in73 mm of precipitation in a typical March.
- Record high
- 86°30° (2026)
- Record low
- −14°−26° (2015)
- Heating degree days
- 770
- Cooling degree days
- 1
Monticello in April
Highs average 63°17° and lows 40°4°, with 3.7 in94 mm of precipitation in a typical April.
- Record high
- 89°32° (2007)
- Record low
- 4°−16° (2018)
- Heating degree days
- 411
- Cooling degree days
- 6
Monticello in May
Highs average 74°23° and lows 51°11°, with 4.6 in116 mm of precipitation in a typical May.
- Record high
- 94°34° (2018)
- Record low
- 26°−3° (2005)
- Heating degree days
- 155
- Cooling degree days
- 70
Monticello in June
Highs average 82°28° and lows 60°15°, with 4.9 in125 mm of precipitation in a typical June.
- Record high
- 99°37° (2022)
- Record low
- 35°2° (2003)
- Heating degree days
- 17
- Cooling degree days
- 194
Monticello in July
Highs average 84°29° and lows 62°17°, with 4.3 in109 mm of precipitation in a typical July.
- Record high
- 99°37° (2012)
- Record low
- 44°7° (2024)
- Heating degree days
- 4
- Cooling degree days
- 247
Monticello in August
Highs average 82°28° and lows 60°15°, with 3.3 in85 mm of precipitation in a typical August.
- Record high
- 96°36° (2012)
- Record low
- 41°5° (2004)
- Heating degree days
- 12
- Cooling degree days
- 196
Monticello in September
Highs average 77°25° and lows 52°11°, with 3.1 in80 mm of precipitation in a typical September.
- Record high
- 98°37° (2011)
- Record low
- 31°−1° (2012)
- Heating degree days
- 94
- Cooling degree days
- 90
Monticello in OctoberThis month
Highs average 65°19° and lows 41°5°, with 3.2 in80 mm of precipitation in a typical October.
- Record high
- 90°32° (2026)
- Record low
- 19°−7° (2018)
- Heating degree days
- 377
- Cooling degree days
- 16
Monticello in November
Highs average 50°10° and lows 31°0°, with 3.1 in78 mm of precipitation in a typical November.
- Record high
- 78°26° (2016)
- Record low
- 1°−17° (2019)
- Heating degree days
- 730
- Cooling degree days
- 1
Monticello in December
Highs average 38°3° and lows 23°−5°, with 2.3 in58 mm of precipitation in a typical December.
- Record high
- 71°22° (2012)
- Record low
- −16°−27° (2025)
- Heating degree days
- 1062
- Cooling degree days
- 0