Photo: Barry Gilfry from Cornpatch, Iowa · CC BY-SA 2.0Hamilton’s winters are colder and snowier than most of the U.S.
A typical July afternoon reaches 86°, a January night drops to 17°, and about 23 inches of snow falls in a normal winter.
A year in Hamilton at a glance
Each month’s typical high and low, and what it brings.
What stands out about Hamilton’s climate
Compared with towns across the U.S., with Hamilton’s place in Illinois beside it.
What a year in Hamilton feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 198 frost-free days a year
In half of years the last 32° night comes by April 10 and the first by October 27. Frost and day counts come from NOAA’s station at Keokuk Lock Dam 19, IA, 0.8 miles from the town’s center, at about the same height.
The 2023 USDA map puts Hamilton’s center in zone 6a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −6°. 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 40 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 Hamilton
84% 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 Keokuk Lock Dam 19, IA.
Living with Hamilton’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
198 frost-free days in zone 6a. The last frost comes by Apr 10 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 27.
Months with highs of 62–84° and lows of 40° or more: April, May, June, September and October. 0.5 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Hamilton from natural hazards, river flooding is the largest share (33%); heat waves, cold waves, winter storms and ice storms together are 39%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Hamilton and its neighbors
Every town next door is within a degree of Hamilton in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Hamilton’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 |
|---|---|---|---|---|
| Hamilton, IL | 17° | 86° | 40" | 23" |
| Savannah, MO | 18° | 87° | 37" | 21" |
| Lock Haven, PA | 19° | 86° | 41" | 30" |
| Peru, IN | 19° | 84° | 40" | 21" |
| Dublin, OH | 21° | 85° | 40" | 24" |
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value. Snow and frost-free days come from the nearest weather station, so neighbors often share them.
Warmer than it used to be
The last 30 years in Hamilton averaged 0.7° warmer than the 1900s. The biggest change is in December (+1.9°).
A smaller shift than in 94% 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 Hamilton compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Hamilton’s place among Illinois’.
Hamilton weather by month
Highs, lows and precipitation from NOAA’s grid at Hamilton’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° | 17° | 1.7" | 7.6" | 8 | 15 | 19° – 38° |
| February | 39° | 22° | 1.9" | 6.3" | 7 | 8 | 18° – 41° |
| March | 51° | 32° | 2.6" | 2.1" | 9 | 2 | 34° – 56° |
| April | 64° | 42° | 4.1" | 0.4" | 11 | 0 | 44° – 60° |
| May | 74° | 53° | 5.2" | 0.0" | 12 | 0 | 58° – 72° |
| June | 83° | 63° | 5.0" | 0.0" | 10 | 0 | 69° – 76° |
| July | 86° | 67° | 4.2" | 0.0" | 9 | 0 | 71° – 83° |
| August | 85° | 64° | 3.8" | 0.0" | 8 | 0 | 69° – 80° |
| September | 78° | 56° | 3.6" | 0.0" | 7 | 0 | 61° – 72° |
| October | 66° | 45° | 3.2" | 0.1" | 8 | 0 | 49° – 60° |
| November | 51° | 33° | 2.6" | 1.4" | 8 | 1 | 34° – 51° |
| December | 39° | 23° | 2.0" | 5.2" | 8 | 6 | 16° – 40° |
| Year | 62° | 43° | 39.8" | 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 7°.
Where Hamilton’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 Hamilton’s center.
- Snow: Bentley, IL.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Keokuk Lock Dam 19, IA, 0.8 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 Hamilton’s climate
What is the weather like in Hamilton?
A typical July afternoon reaches 86°, a January night drops to 17°, and about 23 inches of snow falls in a normal winter. Colder January nights than 73% of U.S. towns; hotter July afternoons than 56% of U.S. towns.
How cold does it get in Hamilton in winter?
January nights average 17°. About 117 nights a year reach 32° or below and 7 reach 0° or below. In the coldest January of the last 30 years the month averaged 19°.
How much snow does Hamilton 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 Hamilton?
July, with a typical high of 86° and a low of 67°. About 26 days a year reach 90° and 1 reach 100° (Keokuk Lock Dam 19, IA).
When is the first and last frost in Hamilton?
In half of years the last spring frost (32°) comes by April 10 and the first fall frost by October 27, about 198 frost-free days, at Keokuk Lock Dam 19, IA.
What growing zone is Hamilton in?
Zone 6a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −6°.
What is the best time of year to visit Hamilton?
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 Hamilton getting warmer?
Yes: 1991–2020 averaged 0.7° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 94% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Hamilton.
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.