Mosquito season in Lake County, IL: when it starts and ends
Mosquito months in Lake County
In a normal year mosquito season in Lake County, IL starts around April 22 and ends around October 22, about 26 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Lake County, and when
- Start tipping out standing water weekly by April 8.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 22.
- 41 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to August, and check IL spray notices.
Lake County against the rest of IL
Lake County has the 93rd longest season of 102 IL counties, at 183 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 49.8°F.
- Kane County: April 19 to October 20 (184 days, 35 WNV)
- Ogle County: April 19 to October 19 (183 days, 1 WNV)
- Lee County: April 20 to October 19 (182 days, 2 WNV)
- McHenry County: April 21 to October 19 (182 days, 11 WNV)
West Nile in Lake County
From 1999 to 2025, CDC ArboNET counted 98 human West Nile cases in Lake County (57 neuroinvasive) across 18 years. The worst was 2025 with 12; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.