Monarch Butterflies in Illinois in September
Yes, September is one of the best months to see monarch butterflies in Illinois. It is the 3rd busiest month of the year, with 3,582 of the 15,827 sightings logged across the year (22.6%), 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.
Peak month for monarch butterflies in Illinois
22.6%
of yearly sightings
3,582
records in September
#3
busiest month of 12
15,827
verified records a year
August 30.2%, September 22.6%, October 4.6%. Busiest month is August at 30.2%.
15,827 verified observations of monarch butterflies in Illinois, recorded across 10 months of the year on iNaturalist.
When monarch butterflies are recorded in Illinois
Peak month
August
4,777 records (30.2% of the year)
| Month | Observations | Share |
|---|---|---|
| January | 0 | 0% |
| February | 1 | 0% |
| March | 0 | 0% |
| April | 47 | 0.3% |
| May | 571 | 3.6% |
| June | 1,750 | 11.1% |
| Julypeak | 4,325 | 27.3% |
| Augustpeak | 4,777 | 30.2% |
| Septemberpeak | 3,582 | 22.6% |
| October | 727 | 4.6% |
| November | 46 | 0.3% |
| December | 1 | 0% |
Monarch Butterflies you are most likely to see
| Species | Verified observations |
|---|---|
| Monarch | 15,827 |
In Illinois, September carries 22.6% of the year's monarch butterflies sightings, about 14.3 points above an even month-to-month split. That makes it the 3rd busiest of the twelve months, out of 10 months with recorded activity.
Activity is easing off from August (30.2%) into September, and it heads toward October (4.6%) after. This is right inside the peak window, so September is one of the surest months to plan a trip around.
The monarch butterflies most often recorded in Illinois are Monarch. 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 monarch butterflies you are most likely to see
- Monarch15,827 records
Plan your monarch butterfly 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 monarch butterfly viewing area.
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Stay nearbyStay near Lewis & Clark National Historic Trail
Compare hotels, cabins and lodges close to the best monarch butterfly viewing area in Illinois.
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Broader backupBook a monarch butterfly tour in Illinois
Compare guided wildlife tours, boat trips and nature experiences if you want a second travel network beyond the live widget.
Frequently asked questions
Can you see monarch butterflies in Illinois in September?+
Yes. September accounts for 3,582 of the 15,827 verified monarch butterflies sightings logged in Illinois across the year, which is 22.6% of the annual total.
Is September a good time to see monarch butterflies in Illinois?+
September is one of the best months. It ranks 3rd of the year and sits inside the peak window of August, July and September.
What month is best for monarch butterflies in Illinois?+
August is the single busiest month, with the broader peak running through August, July and September, based on 15,827 verified observations.
Which monarch butterflies are you most likely to see in Illinois?+
The most-recorded species in Illinois are Monarch, based on all-time iNaturalist counts.
See monarch butterflies in Illinois in other months
More wildlife in Illinois