Best Time to See Bats in Illinois
May, July and August is the best time to see bats in Illinois. Based on 1,340 verified iNaturalist observations, here is exactly when bats are most active across the year in Illinois.
By Tim, founder of Easy Street Markets. I maintain the wildlife database and verify every animal and source myself. Updated June 28, 2026.
Silver-haired Bat · Ronni :) CC BY
Big Brown Bat · Public domain CC0
Silver-haired Bat · Ronni :) CC BY
1,340 verified observations of bats in Illinois, recorded across 12 months of the year on iNaturalist.
When bats are recorded in Illinois
Peak month
May
190 records (14.2% of the year)
| Month | Observations | Share |
|---|---|---|
| January | 22 | 1.6% |
| February | 80 | 6% |
| March | 64 | 4.8% |
| April | 148 | 11% |
| Maypeak | 190 | 14.2% |
| June | 138 | 10.3% |
| Julypeak | 183 | 13.7% |
| Augustpeak | 158 | 11.8% |
| September | 142 | 10.6% |
| October | 144 | 10.7% |
| November | 48 | 3.6% |
| December | 23 | 1.7% |
Bats you are most likely to see
| Species | Verified observations |
|---|---|
| Big Brown Bat | 316 |
| Eastern Red Bat | 295 |
| Silver-haired Bat | 254 |
| Northern Hoary Bat | 74 |
| Tri-coloured Bat | 48 |
| Evening Bat | 30 |
| Little Brown Bat | 28 |
| Indiana Bat | 10 |
Weather to expect, source Open-Meteo
Typical weather in Illinois
Recent typical conditions by month, so you can plan a trip around both when bats are active and what the weather is doing. The best months to look for bats sit around 54 to 85 degrees Fahrenheit, so pack for that.
| Month | Avg high | Avg low | Rain |
|---|---|---|---|
| Jan | 38°F | 23°F | 3" |
| Feb | 40°F | 22°F | 3.1" |
| Mar | 53°F | 34°F | 4.8" |
| Apr | 63°F | 43°F | 4.1" |
| Maybest time | 73°F | 54°F | 4.6" |
| Jun | 83°F | 64°F | 3.5" |
| Julbest time | 85°F | 68°F | 4.3" |
| Augbest time | 83°F | 66°F | 3.9" |
| Sep | 79°F | 61°F | 3" |
| Oct | 65°F | 48°F | 4.9" |
| Nov | 52°F | 35°F | 1.8" |
| Dec | 45°F | 29°F | 2.3" |
Typical recent conditions (5-year means) from the Open-Meteo archive, averaged for Illinois. Weather varies year to year, so treat these as a guide.
More on bats in Illinois:
Sightings of bats in Illinois peak in May, when 190 of the year's 1,340 verified observations are logged — about 14.2% of the annual total. Activity stays high through May, July and August.
The quietest stretch is January and December, when bats are hardest to find — January sees just 22 records. If a reliable sighting matters, plan around the peak window rather than the off-season.
The bats you are most likely to encounter in Illinois are Big Brown Bat, Eastern Red Bat and Silver-haired Bat — the most-recorded species in the state. Each keeps its own seasonal rhythm, but the month-by-month pattern above reflects every reported sighting together.
Where to go
Best places to see bats in Illinois
- Lewis & Clark National Historic Trail — National Historic Trail
- Lincoln Home National Historic Site — National Historic Site
- Emmett Till and Mamie Till-Mobley National Monument — National Monument
- Mormon Pioneer National Historic Trail — National Historic Trail
- New Philadelphia National Historic Site — National Historic Site
- Pullman National Historical Park — National Historical Park
Gear to see them
Frequently asked questions
What is the best month to see bats in Illinois?+
May is the single best month, and the broader peak window runs through May, July and August, based on 1,340 verified iNaturalist observations.
When are bats hardest to see in Illinois?+
January is the quietest month for bats in Illinois, with only 22 verified records.
Are bats active year-round in Illinois?+
Bats are recorded in 12 of 12 months in Illinois, so they can be seen year-round, with a clear peak in May.
More places to see bats
More wildlife in Illinois