Photo: Robb01 · CC BY-SA 3.0Weather without surprises: Mendon keeps close to the norm for U.S. towns
High summer brings afternoon highs near 86°. By January nights alone, it runs colder than 69% of U.S. towns. Decade by decade the climate has edged up, 0.6° above 1901–2000. Seedlings are safe outdoors from about April 14, with the first autumn frost due around October 23.
A year in Mendon at a glance
Each month’s typical high and low, and what it brings.
What stands out about Mendon’s climate
Compared with towns across the U.S., with Mendon’s place in Illinois beside it.
What a year in Mendon feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 191 frost-free days a year
In half of years the last 32° night comes by April 14 and the first by October 23. Frost and day counts come from NOAA’s station at Quincy Rgnl Airport, 12 miles from the town’s center, at about the same height.
The 2023 USDA map puts Mendon’s center in zone 6a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −7°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 23 inches of snow a winter
Snow, measured at Bentley, IL, falls mostly in January. Precipitation (rain plus melted snow) adds up to 39 inches a year; May is the wettest month and January the driest. Rain or snow falls on about 106 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Mendon
83% of the work is heating. Months averaging under 55° run from November through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Quincy Rgnl Airport.
Living with Mendon’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
191 frost-free days in zone 6a. The last frost comes by Apr 14 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Oct 23.
Months with highs of 62–84° and lows of 40° or more: April, May, June, September and October. 0.0 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Mendon from natural hazards, river flooding is the largest share (27%); heat waves, cold waves, winter storms and ice storms together are 31%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Mendon and similar climates
TownRatings has no climate map of the towns around Mendon yet.
Climates most like Mendon’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Mendon, IL | 18° | 86° | 39" | 23" |
| Savannah, MO | 18° | 87° | 37" | 21" |
| Lock Haven, PA | 19° | 86° | 41" | 30" |
| Dublin, OH | 21° | 85° | 40" | 24" |
| Peru, IN | 19° | 84° | 40" | 21" |
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in Mendon averaged 0.6° warmer than the 1900s. The biggest change is in December (+1.8°).
A smaller shift than in 97% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Mendon compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Mendon’s place among Illinois’.
Mendon weather by month
Highs, lows and precipitation from NOAA’s grid at Mendon’s center; snow, wet days and snow on the ground from Bentley, IL. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 34° | 18° | 1.8" | 7.6" | 8 | 15 | 19° – 38° |
| February | 40° | 22° | 1.9" | 6.3" | 7 | 8 | 18° – 42° |
| March | 51° | 32° | 2.5" | 2.1" | 9 | 2 | 34° – 55° |
| April | 64° | 42° | 4.1" | 0.4" | 11 | 0 | 45° – 60° |
| May | 74° | 53° | 5.1" | 0.0" | 12 | 0 | 58° – 72° |
| June | 83° | 63° | 4.8" | 0.0" | 10 | 0 | 69° – 77° |
| July | 86° | 66° | 4.0" | 0.0" | 9 | 0 | 71° – 82° |
| August | 85° | 64° | 4.0" | 0.0" | 8 | 0 | 69° – 80° |
| September | 78° | 56° | 3.4" | 0.0" | 7 | 0 | 62° – 73° |
| October | 65° | 45° | 3.3" | 0.1" | 8 | 0 | 49° – 61° |
| November | 51° | 33° | 2.6" | 1.4" | 8 | 1 | 35° – 51° |
| December | 39° | 23° | 2.0" | 5.2" | 8 | 6 | 16° – 40° |
| Year | 62° | 43° | 39.4" | 23.1" | 106 | 32 |
How much a month can swing
A normal is an average. December swings the most: from 1991 to 2020 its average ranged from 16° to 40°. June is the most reliable, staying within 8°.
Where Mendon’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Mendon’s center.
- Snow: Bentley, IL.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Quincy Rgnl Airport, 12 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Mendon’s climate
What is the weather like in Mendon?
A typical July afternoon reaches 86°, a January night drops to 18°, and about 23 inches of snow falls in a normal winter. Colder January nights than 69% of U.S. towns; hotter July afternoons than 55% of U.S. towns.
How cold does it get in Mendon in winter?
January nights average 18°. About 112 nights a year reach 32° or below and 5 reach 0° or below. In the coldest January of the last 30 years the month averaged 19°.
How much snow does Mendon get?
About 23 inches in a normal winter at Bentley, IL, most of it in January, with snow on the ground about 32 days a year.
How hot does it get in Mendon?
July, with a typical high of 86° and a low of 66°. About 24 days a year reach 90° and 1 reach 100° (Quincy Rgnl Airport).
When is the first and last frost in Mendon?
In half of years the last spring frost (32°) comes by April 14 and the first fall frost by October 23, about 191 frost-free days, at Quincy Rgnl Airport.
What growing zone is Mendon in?
Zone 6a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −7°.
What is the best time of year to visit Mendon?
By one simple rule (highs of 62–84° and lows of 40° or more), April, May, June, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Mendon getting warmer?
Yes: 1991–2020 averaged 0.6° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 97% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Mendon.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.