Chicago, IL Ragweed Pollen
Ragweed pollen in Chicago usually peaks around September, reaching Very High at its worst. Chicago's allergy year is a short, sharp spring and a long ragweed fall: maple and oak in spring, grass through early summer, and ragweed rolling in off the prairie in late summer.
Ragweed is Chicago's defining allergen, peaking in September as prairie and vacant-lot plants across the region let go at once.
Ragweed in Chicago today
Monday, July 27, 2026
Ragweed pollen by month in Chicago
How ragweed usually runs across the year. The current month is outlined.
Managing ragweed season in Chicago
If ragweed is your trigger, start a daily antihistamine like cetirizine (Zyrtec) or loratadine (Claritin) a week or two before the September peak, rather than waiting for symptoms. Keep windows closed on high-count mornings, shower and change clothes after time outside, and run the AC on recirculate in the car.
When symptoms don't ease with over-the-counter medicine, an allergist in Illinois can test whether ragweed is really what you react to and talk through longer-term options like allergy shots.
Sources
More pollen in Chicago
- Chicago grass pollen — peaks June.
- Chicago oak pollen — peaks April.
- Chicago maple pollen — peaks March to April.
- Chicago pollen calendar — every allergen, month by month.
- Chicago pollen count today — live tree, grass, and weed levels with a 5-day forecast.
- Illinois pollen season — the statewide calendar and other cities.
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Sign up for free alertsSeasonal pattern based on Illinois pollen data and local sources. Today's reading updated daily. MyPollenPal