Illinois experiences a classic Midwest pollen season — tree pollen from April through May, grass pollen in June-July, and ragweed from August through October. Chicago consistently sees high counts due to Lake Michigan weather patterns that trap pollen.
Peak pollen season in Illinois: April–September. Primary allergens: Mixed TreesGrassRagweed
Tree pollen is the first major allergen each year in Illinois, typically starting in early spring with cedar and alder, followed by oak and birch through May.
Grass pollen takes over in late spring through early summer, peaking from May to July depending on location within the state.
Ragweed dominates fall allergies in Illinois, typically from August through October. It's the most widespread fall allergen in the US.
The pollen count in Illinois varies by city and season. Peak pollen season runs April–September. Select a city above for live data.
Pollen levels vary across Illinois. Cities in warmer, more humid areas typically see higher counts. Check individual city pages for current levels.
Pollen season in Illinois peaks in April–September. Tree pollen starts in late winter, followed by grass in summer and ragweed in fall.