Bats in Illinois in September
Yes, September is a good month to see bats in Illinois. It is the 6th busiest month of the year, with 142 of the 1,340 sightings logged across the year (10.6%), based on verified iNaturalist records.
By Tim, founder of Easy Street Markets. I maintain the wildlife database and verify every animal and source myself. Updated June 28, 2026.
Good month for bats in Illinois
10.6%
of yearly sightings
142
records in September
#6
busiest month of 12
1,340
verified records a year
August 11.8%, September 10.6%, October 10.7%. Busiest month is May at 14.2%.
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 |
In Illinois, September carries 10.6% of the year's bats sightings, about 2.3 points above an even month-to-month split. That makes it the 6th busiest of the twelve months, out of 12 months with recorded activity.
Activity is easing off from August (11.8%) into September, and it heads toward October (10.7%) after. The busiest month is May (14.2%), so if timing is flexible, that window is the safer bet.
The bats most often recorded in Illinois are Big Brown Bat, Eastern Red Bat and Silver-haired Bat. Those counts are annual totals rather than a September split, so treat them as which species you are likely to encounter, while the month figures above show how many sightings fall in September itself.
Which bats you are most likely to see
- Big Brown Bat316 records
- Eastern Red Bat295 records
- Silver-haired Bat254 records
- Northern Hoary Bat74 records
- Tri-coloured Bat48 records
- Evening Bat30 records
Plan your bat trip in Illinois
Start with live tours near Lewis & Clark National Historic Trail, then compare a nearby stay and a broader wildlife backup before you lock in the trip.
GetYourGuide
Live tours nearbySee live tours near Lewis & Clark National Historic Trail
Use the live GetYourGuide widget to compare local departures and activity styles close to the main bat viewing area.
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Stay nearbyStay near Lewis & Clark National Historic Trail
Compare hotels, cabins and lodges close to the best bat viewing area in Illinois.
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Broader backupBook a bat tour in Illinois
Compare guided wildlife tours, boat trips and nature experiences if you want a second travel network beyond the live widget.
Gear to see them
Frequently asked questions
Can you see bats in Illinois in September?+
Yes. September accounts for 142 of the 1,340 verified bats sightings logged in Illinois across the year, which is 10.6% of the annual total.
Is September a good time to see bats in Illinois?+
September is the 6th busiest month. It is workable, though May and July is the stronger window for a reliable sighting.
What month is best for bats in Illinois?+
May is the single busiest month, with the broader peak running through May, July and August, based on 1,340 verified observations.
Which bats are you most likely to see in Illinois?+
The most-recorded species in Illinois are Big Brown Bat, Eastern Red Bat and Silver-haired Bat, based on all-time iNaturalist counts.
See bats in Illinois in other months
More places to see bats
More wildlife in Illinois