Mosquito season in Boone County, IL: when it starts and ends
Mosquito months in Boone County
In a normal year mosquito season in Boone County, IL starts around April 24 and ends around October 15, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Boone County, and when
- Start tipping out standing water weekly by April 10.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 15.
- 2 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to July, more so if over 60.
Boone County against the rest of IL
Boone County has the 102nd longest season of 102 IL counties, at 174 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 47.2°F.
- Winnebago County: April 23 to October 16 (177 days, 11 WNV)
- Carroll County: April 23 to October 16 (176 days, 2 WNV)
West Nile in Boone County
From 1999 to 2025, CDC ArboNET counted 8 human West Nile cases in Boone County (5 neuroinvasive) across 6 years. The worst was 2008 with 2; the latest was 2025.
More: how the dates are worked out · when mosquitoes go away for the winter.