Today's Mosquito Risk in Illinois: Real-Time Forecast & Activity Map
Check your ZIP code for local mosquito activity, West Nile risk, and prevention insights.
Built from CDC and NOAA data
Mosquito Surveillance Insights
- Annual WNV Cases
- about 100 to 200 confirmed cases annually
- one of the highest absolute counts in the Midwest
- Based on CDC ArboNET surveillance data
- Risk Tier
- Tier 3: Moderate
- Chicago heat island sustains some of the densest Cx. pipiens populations in the country.
- Per mosquito-risk-model regional tier
- Highest-Risk Areas
- Cook, DuPage, Kane, Lake, Will (WNV); Sangamon and Peoria (central Illinois)
Current Situation in Illinois
Illinois carries one of the heaviest absolute WNV burdens in the Midwest, with roughly 100 to 200 confirmed human cases in a typical year. Cook County alone often accounts for more than 30% of the statewide count, with the Chicago metro's dense Cx. pipiens populations breeding in storm drains, rowhouse alley catch basins, and abandoned industrial lots driving sustained August transmission. Aedes albopictus is established across the southern half of the state. EEE is rare. The Mississippi and Illinois River floodplains produce massive Aedes vexans hatches after summer storms, and the Calumet wetlands south of Chicago hold steady seasonal populations. Shawnee National Forest in the far south and the Cache River bottoms produce woodland Aedes off beaver ponds. Biting season runs June through September.
Snapshot of the current mosquito situation in Illinois, drawn from CDC ArboNET surveillance and the regional risk model.
- Risk Level
- High
- Peak Activity
- June through September
- Dominant Vector
- Northern House Mosquito (Culex pipiens)
Where Mosquitoes Breed in Illinois
Illinois mosquito habitat is anchored by the Chicago metro storm-drain grid, the Mississippi and Illinois River floodplains, and the southern swamps. The Cook County wetlands, Calumet River corridor, and Lake Calumet sustain dense Cx. pipiens populations through summer, with Chicago's heat island stretching biting into early October. The Illinois River bottomlands from Peoria through Pekin and the Mississippi River floodplain along the western border produce enormous Aedes vexans hatches after summer storms. The Chicago River corridor and the urban catch basins across Aurora, Joliet, and Rockford carry the suburban Cx. pipiens load. Shawnee National Forest hollows and the Cache River cypress swamps in Pulaski and Johnson counties hold woodland Aedes and the southernmost Aedes albopictus populations in the state.
Hotspot Counties & Areas
- Cook County (Chicago metro, Calumet wetlands)
- DuPage County (western Chicago suburbs)
- Kane County (Aurora, Fox River)
- Will County (Joliet)
- Winnebago County (Rockford)
- Sangamon County (Springfield)
- Peoria County (Illinois River floodplain)
- Shawnee National Forest and Cache River swamps
Seasonal Activity Pattern
Biting starts in early June, peaks late July through August, and tapers through September. WNV cases concentrate in August across Cook County and the collar counties of DuPage, Kane, Lake, and Will, with the Chicago heat island sustaining transmission into early October. Springfield and the central Illinois agricultural counties see steady August Cx. pipiens pressure. Aedes albopictus daytime biting in suburban yards across the southern half of the state runs heavy from July through September. Heavy summer storms produce floodwater Aedes pulses along the Mississippi and Illinois River bottomlands. Shawnee National Forest hollows run a week or two behind the metros on phenology.
Monthly Biting Intensity (Midwest)
Illinois Mosquito Risk Profile
- WNV burden level
- High
- about 100 to 200 confirmed cases annually; one of the highest absolute counts in the Midwest
- EEE risk
- Rare
- Peak biting season
- late May through September
- Top urban risk areas
- Chicago (Cook)
- Aurora (Kane)
- Rockford (Winnebago)
- Springfield (Sangamon)
Signature habitat: Chicago metro storm drains, Mississippi and Illinois River floodplains, southern Illinois swamps.
Climate driver: Chicago heat island sustains some of the densest Cx. pipiens populations in the country.
Check Your Local Mosquito Risk
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Common Mosquitoes in Illinois
Understanding which mosquitoes are active in Illinois helps you identify threats and take appropriate precautions. Click any card for details.
Northern House Mosquito
Culex pipiens
Risk: West Nile virus, St. Louis encephalitis, dog heartworm.
Key feature: Medium brown body with banded abdomen. Looks nearly identical to Cx. quinquefasciatus.
Active: Late spring through early fall in the north. Adult females overwinter in basements, garages, and storm drains.
Inland Floodwater Mosquito
Aedes vexans
Risk: Aggressive nuisance biter. Weak vector for West Nile, dog heartworm.
Key feature: Brown body with pale bands on the legs and a tapered abdomen.
Active: Spring through fall. Population spikes a week or two after major rain events.
West Nile Virus
Vector: Northern House Mosquito
West Nile Virus
The dominant West Nile vector across the northern half of the US. About 80% of infections are asymptomatic.
What to watch for
- Onset typically 2 to 15 days after a bite
- Most cases mild or asymptomatic, small fraction severe
- Neurological signs (severe headache, neck stiffness, confusion) need ER care
Breaking the Cycle in Illinois
The mosquito lifecycle takes about a week. These habits cut local biting pressure faster than anything else, building multiple layers of protection.
Drain the Yard Weekly
Empty buckets, planter saucers, kiddie pools, tarps, and clogged gutters. A week of standing water is one full mosquito generation.
Repel Before Going Out
EPA-registered DEET (20-30%), picaridin (20%), IR3535, or oil of lemon eucalyptus. Apply before going outside, especially at dusk and dawn.
Seal the House
Window and door screens with no tears. AC and porch fans both work. Mosquitoes struggle to fly upwind even at 1-2 mph air speed.
Treat Outdoor Clothing
Permethrin-treated long sleeves and pants for evening yard work, hiking, or fishing. Remains effective through 70+ wash cycles.
If You Develop Symptoms
Most mosquito bites are harmless. A small fraction can transmit illness, and knowing the timeline matters more than panicking at every itch.Five things to know.
Watch for fever
Fever, body aches, headache, or fatigue 2 to 15 days after a bite. West Nile often feels like flu, and most infections never get diagnosed.
Note where and when
A rough record of where and when you got bitten helps your doctor decide what to test for. Date, location, mosquito-heavy areas you visited.
Get help fast for neuro signs
Severe headache, neck stiffness, confusion, vision changes, or sudden muscle weakness can mean neuroinvasive WNV or EEE. Both are medical emergencies.
Pregnant exposure?
If pregnant and bitten in an area with documented Zika or local dengue transmission, mention to your OB. Same goes for travel exposure.
Children and seniors
Higher risk of severe disease from WNV, EEE, and dengue in adults over 60 and children under 5. Early call to the pediatrician or PCP if symptoms appear.
When does mosquito season end in Illinois?
Mosquito activity winds down after the first hard freeze, which in Illinois typically arrives around Oct 16. See the local first-frost window and city-by-city freeze dates.
Illinois first frost datesAlso worried about ticks in Illinois?
Lyme disease risk and tick activity track different seasonal patterns than mosquitoes. See your Illinois tick forecast.
View Illinois tick forecastStay Safe in Illinois
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