Mosquito season in Grant County, WI: when it starts and ends
Mosquito months in Grant County
In a normal year mosquito season in Grant County, WI starts around April 24 and ends around October 14, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Grant County, and when
- Start tipping out standing water weekly by April 10.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 14.
- No West Nile cases since 2016, so bites in Grant County are a nuisance; check window screens.
Grant County against the rest of WI
Grant County has the 11th longest season of 72 WI counties, at 173 days against 180 in La Crosse County and 139 in Rusk County. Its mean temperature is 46.4°F.
- Jefferson County: April 25 to October 16 (174 days, 7 WNV)
- Buffalo County: April 23 to October 13 (173 days, 1 WNV)
- Sauk County: April 24 to October 15 (173 days, 0 WNV)
- Racine County: April 30 to October 20 (173 days, 4 WNV)
West Nile in Grant County
From 1999 to 2025, CDC ArboNET counted 5 human West Nile cases in Grant County (3 neuroinvasive) across 4 years. The worst was 2006 with 2; the latest was 2012.
See how the dates are worked out, and when mosquitoes go away for the winter.