Mosquito season in Henry County, IL: when it starts and ends
Mosquito months in Henry County
In a normal year mosquito season in Henry County, IL starts around April 14 and ends around October 22, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Henry 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 22.
- No West Nile cases since 2016, so bites in Henry County are a nuisance; check window screens.
Henry County against the rest of IL
Henry County has the 81st longest season of 102 IL counties, at 191 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 50.4°F.
- McLean County: April 14 to October 23 (192 days, 4 WNV)
- Grundy County: April 15 to October 23 (192 days, 2 WNV)
- LaSalle County: April 14 to October 22 (191 days, 4 WNV)
- Knox County: April 14 to October 21 (190 days, 1 WNV)
West Nile in Henry County
From 1999 to 2025, CDC ArboNET counted 5 human West Nile cases in Henry County (2 neuroinvasive) across 4 years. The worst was 2002 with 2; the latest was 2012.
More: how the dates are worked out · when the season starts across the US.