Mosquito season in Monroe County, WI: when it starts and ends

Mosquito months in Monroe County

In a normal year mosquito season in Monroe County, WI starts around April 29 and ends around October 8, about 23 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Monroe County, and when

• Start tipping out standing water weekly by April 15.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 8.
• 2 West Nile cases since 2016 (last 2017): you should use repellent at dusk July to July, more so if over 60.

Monroe County against the rest of WI

Monroe County has the 33rd longest season of 72 WI counties, at 162 days against 180 in La Crosse County and 139 in Rusk County. Its mean temperature is 44.6°F.

• Polk County: April 29 to October 9 (163 days, 0 WNV)
• Waushara County: April 30 to October 10 (163 days, 0 WNV)
• Chippewa County: April 30 to October 9 (162 days, 2 WNV)
• Dunn County: April 30 to October 9 (162 days, 2 WNV)

West Nile in Monroe County

From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Monroe County (2 neuroinvasive) across 1 year. The worst was 2017 with 2; the latest was 2017.

See how the dates are worked out, and when mosquitoes go away for the winter.