Mosquito season in De Witt County, IL: when it starts and ends
Mosquito months in De Witt County
In a normal year mosquito season in De Witt County, IL starts around April 9 and ends around October 24, about 28 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in De Witt County, and when
- Start tipping out standing water weekly by March 26.
- Book any yard treatment for early April, ahead of the July peak.
- Repellent can go away after October 24.
- No West Nile cases since 2016, so bites in De Witt County are a nuisance; check window screens.
De Witt County against the rest of IL
De Witt County has the 64th longest season of 102 IL counties, at 198 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 51.8°F.
- Champaign County: April 9 to October 26 (200 days, 5 WNV)
- Peoria County: April 9 to October 25 (199 days, 12 WNV)
- Henderson County: April 10 to October 25 (198 days, 0 WNV)
- Schuyler County: April 10 to October 25 (198 days, 0 WNV)
West Nile in De Witt County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in De Witt County (1 neuroinvasive) across 1 year. The worst was 2002 with 1; the latest was 2002.
More: how the dates are worked out · when the season starts across the US.