Mosquito season in Washington County, IL: when it starts and ends
Mosquito months in Washington County
In a normal year mosquito season in Washington County, IL starts around March 31 and ends around November 2, about 31 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Washington County, and when
- Start tipping out standing water weekly by March 17.
- Book any yard treatment for late March, ahead of the July peak.
- Repellent can go away after November 2.
- No West Nile cases since 2016, so bites in Washington County are a nuisance; check window screens.
Washington County against the rest of IL
Washington County has the 18th longest season of 102 IL counties, at 216 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 55.1°F.
- Jackson County: March 30 to November 1 (216 days, 3 WNV)
- Clay County: March 31 to November 2 (216 days, 0 WNV)
- Bond County: March 31 to November 2 (215 days, 1 WNV)
- Randolph County: April 1 to November 1 (214 days, 1 WNV)
West Nile in Washington County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Washington County (1 neuroinvasive) across 1 year. The worst was 2013 with 1; the latest was 2013.
See how the dates are worked out, and when the season starts across the US.