Mosquito season in Knox County, IL: when it starts and ends
Mosquito months in Knox County
In a normal year mosquito season in Knox County, IL starts around April 14 and ends around October 21, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Knox County, and when
- Start tipping out standing water weekly by March 31.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 21.
- 1 West Nile case since 2016 (last 2020): you should use repellent at dusk June to August, more so if over 60.
Knox County against the rest of IL
Knox County has the 83rd longest season of 102 IL counties, at 190 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 50.2°F.
- Henry County: April 14 to October 22 (191 days, 0 WNV)
- LaSalle County: April 14 to October 22 (191 days, 4 WNV)
- Will County: April 16 to October 23 (190 days, 34 WNV)
- Mercer County: April 15 to October 21 (189 days, 1 WNV)
West Nile in Knox County
From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Knox County (1 neuroinvasive) across 2 years. The worst was 2020 with 1; the latest was 2020.
Background: when the season starts across the US; how the dates are worked out.