Mosquito season in Union County, IL: when it starts and ends
Mosquito months in Union County
In a normal year mosquito season in Union County, IL starts around March 29 and ends around November 8, about 32 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Union County, and when
- Start tipping out standing water weekly by March 15.
- Book any yard treatment for late March, ahead of the July peak.
- Repellent can go away after November 8.
- No West Nile cases since 2016, so bites in Union County are a nuisance; check window screens.
Union County against the rest of IL
Union County has the 5th longest season of 102 IL counties, at 224 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 58.5°F.
- Gallatin County: March 26 to November 5 (224 days, 0 WNV)
- Madison County: March 27 to November 6 (224 days, 9 WNV)
- Alexander County: March 26 to November 4 (223 days, 0 WNV)
- Edwards County: March 27 to November 5 (223 days, 1 WNV)
West Nile in Union County
CDC ArboNET lists no human West Nile cases for Union County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 9 of those years.
More: how the dates are worked out · when mosquitoes go away for the winter.