Pollen Count in Joliet, IL

Joliet, Illinois, sits in the humid continental climate zone of the upper Midwest, where distinct seasons produce a prolonged and varied allergy calendar for local residents. The season typically begins in late March and runs through October, driven by the region's mix of oak-hickory woodlands, agricultural surroundings, and river valley moisture from the Des Plaines and Kankakee watersheds.

Tree pollen kicks off the year, with oak, maple, birch, elm, cottonwood, ash, and walnut peaking from April through May and producing some of the heaviest airborne counts of the year. As trees taper off, grass pollen takes over from late May through July, dominated by Kentucky bluegrass, timothy, orchard grass, and ryegrass—all thriving in Will County's lawns and pasturelands.

By mid-August, weed pollen becomes the primary irritant, with short and giant ragweed leading the way alongside lamb's quarters, pigweed, and plantain, typically persisting until the first hard frost in October. Overlap between late-spring trees and early grasses often intensifies May symptoms.

Non-pollen triggers are also significant: humid summers promote outdoor mold spores (Alternaria, Cladosporium), while winter brings indoor dust mite concerns.

Overall, Joliet's allergy profile is defined by a long, layered season marked by heavy grass and ragweed exposure.