Mosquito season in Henderson County, IL: when it starts and ends
Mosquito months in Henderson County
In a normal year mosquito season in Henderson County, IL starts around April 10 and ends around October 25, about 28 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Henderson County, and when
- Start tipping out standing water weekly by March 27.
- Book any yard treatment for early April, ahead of the July peak.
- Repellent can go away after October 25.
- No West Nile cases since 2016, so bites in Henderson County are a nuisance; check window screens.
Henderson County against the rest of IL
Henderson County has the 65th longest season of 102 IL counties, at 198 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 51.7°F.
- Peoria County: April 9 to October 25 (199 days, 12 WNV)
- De Witt County: April 9 to October 24 (198 days, 0 WNV)
- Schuyler County: April 10 to October 25 (198 days, 0 WNV)
- Edgar County: April 11 to October 25 (197 days, 2 WNV)
West Nile in Henderson County
From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Henderson County (1 neuroinvasive) across 1 year. The worst was 2002 with 2; the latest was 2002.
See how the dates are worked out, and when the season starts across the US.