Hennepin, Illinois climate: Normal weather by month, frost dates and records
Hennepin's normal year runs from 17°F January nights to 85°F July afternoons, with 38.6 inches of precipitation a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 10.8°C, January lows of −8°C, July highs of 29°C, 980 mm of precipitation a year.
- NOAA stationHennepin
- Station IDUSC00114012
- Location41.25°N 89.34°W
- Elevation515 ft (157 m)
- From the center1 miles
- Population747
On October 23, the normal high in Hennepin is 62°F and the normal low 40°F.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Hennepin.
- Jan 32° 17°
- Feb 37° 20°
- Mar 50° 30°
- Apr 64° 41°
- May 74° 51°
- Jun 82° 61°
- Jul 85° 65°
- Aug 83° 62°
- Sep 77° 55°
- Oct 65° 43°
- Nov 50° 32°
- Dec 37° 22°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Hennepin each month?
July is the warmest month, with normal highs of 85°F; January the coldest, with normal lows of 17°F. The most precipitation falls in May (4.76 in), the least in February (1.80 in).
| Month | High | Low | Mean | Precip. | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|
| January | 32°F | 17°F | 24.6°F | 1.95 | – | <1 | 28 | 9 h 30 min |
| February | 37°F | 20°F | 28.6°F | 1.80 | – | <1 | 24 | 10 h 40 min |
| March | 50°F | 30°F | 40.1°F | 2.46 | – | <1 | 18 | 11 h 50 min |
| April | 64°F | 41°F | 52.0°F | 3.85 | – | <1 | 6 | 13 h 20 min |
| May | 74°F | 51°F | 62.5°F | 4.76 | – | 1 | <1 | 14 h 30 min |
| June | 82°F | 61°F | 71.6°F | 4.55 | – | 3 | <1 | 15 h 10 min |
| July | 85°F | 65°F | 74.5°F | 3.89 | – | 6 | <1 | 14 h 50 min |
| August | 83°F | 62°F | 72.7°F | 3.77 | – | 3 | <1 | 13 h 50 min |
| September | 77°F | 55°F | 65.8°F | 3.45 | – | 3 | <1 | 12 h 30 min |
| October | 65°F | 43°F | 54.1°F | 3.31 | – | <1 | 3 | 11 h 10 min |
| November | 50°F | 32°F | 41.1°F | 2.60 | – | <1 | 16 | 9 h 50 min |
| December | 37°F | 22°F | 29.3°F | 2.19 | – | <1 | 24 | 9 h 10 min |
| Year (annual) | 61°F | 42°F | 51.4°F | 38.58 | – | 17 | 119 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. |
|---|---|---|---|---|
| January | 0°C | −8°C | −4.1°C | 50 mm |
| February | 3°C | −7°C | −1.9°C | 46 mm |
| March | 10°C | −1°C | 4.5°C | 62 mm |
| April | 18°C | 5°C | 11.1°C | 98 mm |
| May | 23°C | 11°C | 16.9°C | 121 mm |
| June | 28°C | 16°C | 22.0°C | 116 mm |
| July | 29°C | 18°C | 23.6°C | 99 mm |
| August | 28°C | 17°C | 22.6°C | 96 mm |
| September | 25°C | 13°C | 18.8°C | 88 mm |
| October | 18°C | 6°C | 12.3°C | 84 mm |
| November | 10°C | 0°C | 5.1°C | 66 mm |
| December | 3°C | −6°C | −1.5°C | 56 mm |
NOAA publishes no 1991-2020 snowfall normal for this station. The nearest record that keeps one, Princeton (10 miles away), gets 29 inches of snow in a normal year; elevation and distance can change that.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00114012; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Hennepin?
Normal highs sit between 65°F and 85°F in May, June, July, August, September and October.
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00114012.
When is the last frost in Hennepin?
In Hennepin, the last spring frost (32°F) comes after April 18 in half of years and after May 3 in one year in ten; the first autumn frost comes before October 22 in half of years and before October 7 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 181 year in 10 after May 3; 9 in 10 after April 3
- First autumn frost, half of years before
- October 221 year in 10 before October 7; 9 in 10 before November 3
NOAA puts the median frost-free season at 188 days, and the season without a hard freeze (28°F) at 211 days.
A hard freeze (28°F) comes after April 6 in half of springs and before November 1 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Hennepin in zone 5b in ZIP code 61327.
Frost dates for every NOAA station in Illinois · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00114012; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get in Hennepin?
In a normal year in Hennepin, 17 days a year reach 90°F (1 of them 100°F or more) and 119 nights fall to 32°F or colder.
- Days at 90°F or more
- 17a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 119a normal year
- Days that stay below freezing
- 33high of 32°F or less
Source: NOAA NCEI 1991-2020 annual normals, station USC00114012.
How sunny is Hennepin?
Over a year 74% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Hennepin, 4.0 kWh per square metre a day. July is the sunniest month (81%) and December the cloudiest (63%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 64% | 1.8 |
| February | 68% | 2.7 |
| March | 68% | 3.7 |
| April | 70% | 4.8 |
| May | 72% | 5.5 |
| June | 77% | 6.2 |
| July | 81% | 6.3 |
| August | 80% | 5.5 |
| September | 80% | 4.5 |
| October | 72% | 3.0 |
| November | 68% | 2.0 |
| December | 63% | 1.5 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Hennepin need?
A normal year in Hennepin brings 5,869 heating degree days, 9% more than the median U.S. place (5,373), and 946 cooling degree days, 4% more than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 3,387 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,254 | 0 |
| February | 1,019 | 0 |
| March | 775 | 3 |
| April | 396 | 6 |
| May | 145 | 67 |
| June | 11 | 207 |
| July | 2 | 296 |
| August | 6 | 243 |
| September | 83 | 107 |
| October | 352 | 14 |
| November | 718 | 1 |
| December | 1,108 | 0 |
| Year (annual) | 5,869 | 946 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00114012. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Hennepin been warmer than normal lately?
2025 averaged 52.9°F, 1.5°F above the 1991-2020 normal of 51.4°F. 3 of the 4 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 52.9°F | +1.5°F | 39.08 |
| 2022 | 51.0°F | −0.4°F | 37.69 |
| 2024 | 54.7°F | +3.3°F | 38.83 |
| 2025 | 52.9°F | +1.5°F | 31.87 |
Source: observed years: ACIS, station USC00114012. A year counts only with all twelve months complete.
How does Hennepin's climate compare?
Hennepin is warmer than 64 of the other 143 places with their own NOAA record in Illinois, and wetter than 45. Across the 7,247 U.S. stations with normals, its annual mean of 51.4°F is warmer than 47%.
In the Köppen classification computed from these normals, Hennepin is Dfa: continental, no dry season, hot summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Hennepin share this climate record?
8 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- De Pue, IL1,573 people · 6 mi N
- Granville, IL1,331 people · 6 mi E
- Mark, IL507 people · 4 mi E
- Seatonville, IL312 people · 8 mi NE
- Bureau Junction, IL278 people · 3 mi NW
- McNabb, IL274 people · 9 mi SE
- Magnolia, IL254 people · 12 mi SE
- Hollowayville, IL44 people · 8 mi N
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
What do Hennepin's other NOAA stations record?
One more NOAA station keeps 1991-2020 normals in or near Hennepin. This page uses Hennepin; the other differs by site and elevation:
| Station | From the center | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Hennepin Water Treatment Plant USC00114013 | 2 mi NW | 460 ft | 51.0°F | 15°F | 86°F | – | – | April 24 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about Hennepin's climate
What is the coldest month in Hennepin?
January, with a normal high of 32°F and a normal low of 17°F. The warmest is July (85°F by day, 65°F at night).
Does it snow in Hennepin?
Yes. NOAA publishes no 1991-2020 snowfall normal for Hennepin's NOAA station; the nearest record that keeps one, Princeton (10 miles away), records 29 inches of snow in a normal year.
What is the rainiest month in Hennepin?
May, with 4.76 in of precipitation in a normal year; the driest is February with 1.80 in.
What plant hardiness zone is Hennepin in?
The USDA's 2023 map puts Hennepin in zone 5b in ZIP code 61327.
How late can frost come in Hennepin?
In half of years the last 32°F night comes after April 18; in one year in ten it comes after May 3. Waiting until May 3 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Illinois climateThe statewide normals and every place in the state
- Princeton, IL10 miles from this station, 49.7°F a year
- Peru, IL14 miles from this station, 49.6°F a year
- Lacon, IL17 miles from this station, 52.6°F a year
- Ottawa, IL23 miles from this station, 50.2°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made