Mosquito season in Milwaukee County, WI: when it starts and ends
Mosquito months in Milwaukee County
In a normal year mosquito season in Milwaukee County, WI starts around April 28 and ends around October 21, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Milwaukee County, and when
- Start tipping out standing water weekly by April 14.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 21.
- 29 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to August, and check WI spray notices.
Milwaukee County against the rest of WI
Milwaukee County has the 5th longest season of 72 WI counties, at 176 days against 180 in La Crosse County and 139 in Rusk County. Its mean temperature is 48.5°F.
- Walworth County: April 23 to October 17 (177 days, 4 WNV)
- Rock County: April 23 to October 16 (176 days, 6 WNV)
- Crawford County: April 23 to October 15 (175 days, 2 WNV)
- Green County: April 23 to October 15 (175 days, 1 WNV)
West Nile in Milwaukee County
From 1999 to 2025, CDC ArboNET counted 89 human West Nile cases in Milwaukee County (73 neuroinvasive) across 20 years. The worst was 2012 with 27; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.