Best Time to See Monarch Butterflies in Illinois
August, July and September is the best time to see monarch butterflies in Illinois. Based on 15,827 verified iNaturalist observations, here is exactly when monarch butterflies 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.
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 |
Weather to expect, source Open-Meteo
Typical weather in Illinois
Recent typical conditions by month, so you can plan a trip around both when monarch butterflies are active and what the weather is doing. The best months to look for monarch butterflies sit around 61 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" |
| May | 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" |
| Sepbest time | 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 monarch butterflies in Illinois:
Sightings of monarch butterflies in Illinois peak in August, when 4,777 of the year's 15,827 verified observations are logged — about 30.2% of the annual total. Activity stays high through August, July and September.
The quietest stretch is January, March and February, when monarch butterflies are hardest to find — no verified records exist for January. If a reliable sighting matters, plan around the peak window rather than the off-season.
The monarch butterflies you are most likely to encounter in Illinois are Monarch — 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 monarch butterflies 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
Frequently asked questions
What is the best month to see monarch butterflies in Illinois?+
August is the single best month, and the broader peak window runs through August, July and September, based on 15,827 verified iNaturalist observations.
When are monarch butterflies hardest to see in Illinois?+
January is the quietest month for monarch butterflies in Illinois, with no verified records on iNaturalist.
Are monarch butterflies active year-round in Illinois?+
Monarch butterflies are recorded in 10 of 12 months in Illinois, concentrated around August and July.
More places to see monarch butterflies
More wildlife in Illinois