Photo: Languageteaching on Flickr · CC BY 2.0Nights turn raw in Eureka each January, colder than in 79% of U.S. towns
On a normal July day the thermometer tops out near 85°. From frosty January to warm July, readings climb 69°. Precipitation is light here, less than falls on 66% of U.S. towns. Picnics, hikes and garden evenings come into their own from May to June and August to October, with highs of 65–83°.
A year in Eureka at a glance
Each month’s typical high and low, and what it brings.
What stands out about Eureka’s climate
Compared with towns across the U.S., with Eureka’s place in Illinois beside it.
What a year in Eureka feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 178 frost-free days a year
In half of years the last 32° night comes by April 21 and the first by October 17. Frost and day counts come from NOAA’s station at Congerville 2nw, IL, 7 miles from the town’s center, at about the same height.
The 2023 USDA map puts Eureka’s center in zone 5b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −11°. 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 21 inches of snow a winter
Snow, measured at Eureka, IL, falls mostly in February. Precipitation (rain plus melted snow) adds up to 38 inches a year; May is the wettest month and February the driest. Rain or snow falls on about 112 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Eureka
84% of the work is heating. Months averaging under 55° run from October 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 Congerville 2nw, IL.
Living with Eureka’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
178 frost-free days in zone 5b. The last frost comes by Apr 21 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 17.
Months with highs of 62–84° and lows of 40° or more: May, June, August, September and October. 0.7 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Eureka from natural hazards, river flooding is the largest share (53%); heat waves, cold waves, winter storms and ice storms together are 25%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Eureka and its neighbors
Every town next door is within a degree of Eureka in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Eureka’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 |
|---|---|---|---|---|
| Eureka, IL | 16° | 85° | 38" | 21" |
| Centerville, IA | 15° | 85° | 38" | 22" |
| Defiance, OH | 19° | 85° | 37" | 24" |
| Peru, IN | 19° | 84° | 40" | 21" |
| Kirksville, MO | 17° | 86° | 41" | 19" |
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 Eureka averaged 1.6° warmer than the 1900s. The biggest change is in December (+2.8°).
A bigger shift than in 63% 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 Eureka compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Eureka’s place among Illinois’.
Eureka weather by month
Highs, lows and precipitation from NOAA’s grid at Eureka’s center; snow, wet days and snow on the ground from Eureka, IL. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 33° | 16° | 2.1" | 5.2" | 9 | 17° – 36° |
| February | 38° | 20° | 1.8" | 6.3" | 9 | 16° – 40° |
| March | 50° | 30° | 2.6" | 3.1" | 9 | 32° – 54° |
| April | 63° | 39° | 3.8" | 0.3" | 11 | 43° – 58° |
| May | 74° | 51° | 4.6" | 0.0" | 12 | 56° – 71° |
| June | 83° | 60° | 4.2" | 0.0" | 10 | 67° – 75° |
| July | 85° | 64° | 4.2" | 0.0" | 9 | 69° – 81° |
| August | 83° | 62° | 3.7" | 0.0" | 9 | 67° – 78° |
| September | 78° | 54° | 3.3" | 0.0" | 7 | 60° – 71° |
| October | 65° | 42° | 3.1" | 0.0" | 10 | 49° – 60° |
| November | 50° | 32° | 2.7" | 1.4" | 8 | 33° – 50° |
| December | 38° | 22° | 2.2" | 4.9" | 8 | 16° – 40° |
| Year | 62° | 41° | 38.3" | 21.2" | 112 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 16° to 40°. June is the most reliable, staying within 8°.
Where Eureka’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 Eureka’s center.
- Snow: Eureka, IL (NOAA station in town).
- Frost, freezing nights, 90° and 100° days, heating and cooling: Congerville 2nw, IL, 7 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 Eureka’s climate
What is the weather like in Eureka?
A typical July afternoon reaches 85°, a January night drops to 16°, and about 21 inches of snow falls in a normal winter. Colder January nights than 79% of U.S. towns; cooler July afternoons than 50% of U.S. towns.
How cold does it get in Eureka in winter?
January nights average 16°. About 134 nights a year reach 32° or below and 9 reach 0° or below. In the coldest January of the last 30 years the month averaged 17°.
How much snow does Eureka get?
About 21 inches in a normal winter at Eureka, IL, most of it in February.
How hot does it get in Eureka?
July, with a typical high of 85° and a low of 64°. About 24 days a year reach 90° (Congerville 2nw, IL).
When is the first and last frost in Eureka?
In half of years the last spring frost (32°) comes by April 21 and the first fall frost by October 17, about 178 frost-free days, at Congerville 2nw, IL.
What growing zone is Eureka in?
Zone 5b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −11°.
What is the best time of year to visit Eureka?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, August, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Eureka getting warmer?
Yes: 1991–2020 averaged 1.6° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 63% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Eureka.
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.