Mosquito season in Winnebago County, WI: when it starts and ends
Mosquito months in Winnebago County
In a normal year mosquito season in Winnebago County, WI starts around April 27 and ends around October 14, about 24 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Winnebago County, and when
- Start tipping out standing water weekly by April 13.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 14.
- 2 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to July, more so if over 60.
Winnebago County against the rest of WI
Winnebago County has the 17th longest season of 72 WI counties, at 170 days against 180 in La Crosse County and 139 in Rusk County. Its mean temperature is 46.3°F.
- Lafayette County: April 25 to October 13 (171 days, 1 WNV)
- Fond du Lac County: April 27 to October 14 (171 days, 4 WNV)
- Waukesha County: April 28 to October 15 (170 days, 15 WNV)
- Marquette County: April 27 to October 12 (168 days, 0 WNV)
West Nile in Winnebago County
From 1999 to 2025, CDC ArboNET counted 8 human West Nile cases in Winnebago County (2 neuroinvasive) across 7 years. The worst was 2003 with 2; the latest was 2025.
Background: when mosquitoes go away for the winter; how the dates are worked out.