Mosquito season in Will County, IL: when it starts and ends
Mosquito months in Will County
In a normal year mosquito season in Will County, IL starts around April 16 and ends around October 23, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Will County, and when
- Start tipping out standing water weekly by April 2.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 23.
- 34 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check IL spray notices.
Will County against the rest of IL
Will County has the 84th longest season of 102 IL counties, at 190 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 50.4°F.
- LaSalle County: April 14 to October 22 (191 days, 4 WNV)
- Knox County: April 14 to October 21 (190 days, 1 WNV)
- Mercer County: April 15 to October 21 (189 days, 1 WNV)
- Stark County: April 15 to October 21 (189 days, 0 WNV)
West Nile in Will County
From 1999 to 2025, CDC ArboNET counted 105 human West Nile cases in Will County (66 neuroinvasive) across 19 years. The worst was 2006 with 18; the latest was 2025.
See how the dates are worked out, and reading the West Nile counts.