Mosquito season in Lee County, IL: when it starts and ends
Mosquito months in Lee County
In a normal year mosquito season in Lee County, IL starts around April 20 and ends around October 19, about 26 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Lee County, and when
- Start tipping out standing water weekly by April 6.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 19.
- 2 West Nile cases since 2016 (last 2023): you should use repellent at dusk July to August, more so if over 60.
Lee County against the rest of IL
Lee County has the 94th longest season of 102 IL counties, at 182 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 48.5°F.
- Ogle County: April 19 to October 19 (183 days, 1 WNV)
- Lake County: April 22 to October 22 (183 days, 41 WNV)
- McHenry County: April 21 to October 19 (182 days, 11 WNV)
- Whiteside County: April 19 to October 18 (181 days, 1 WNV)
West Nile in Lee County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Lee County (3 neuroinvasive) across 3 years. The worst was 2023 with 1; the latest was 2023.
Background: when the season starts across the US; how the dates are worked out.