Mosquito season in Clay County, IL: when it starts and ends
Mosquito months in Clay County
In a normal year mosquito season in Clay 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 Clay 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 Clay County are a nuisance; check window screens.
Clay County against the rest of IL
Clay County has the 17th longest season of 102 IL counties, at 216 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 55.4°F.
- Williamson County: March 29 to November 1 (217 days, 3 WNV)
- Jackson County: March 30 to November 1 (216 days, 3 WNV)
- Washington County: March 31 to November 2 (216 days, 0 WNV)
- Bond County: March 31 to November 2 (215 days, 1 WNV)
West Nile in Clay County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Clay County (0 neuroinvasive) across 1 year. The worst was 2006 with 1; the latest was 2006.
More: how the dates are worked out · when mosquitoes go away for the winter.