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

Mosquito months in Iron County

In a normal year mosquito season in Iron County, WI starts around May 11 and ends around September 30, about 20 weeks.

What to do in Iron County, and when

Start tipping out standing water weekly by April 27.
Book any yard treatment for mid May, ahead of the July peak.
Repellent can go away after September 30.
No West Nile cases since 2016, so bites in Iron County are a nuisance; check window screens.

Iron County against the rest of WI

Iron County has the 66th longest season of 72 WI counties, at 143 days against 180 in La Crosse County and 139 in Rusk County. Its mean temperature is 40.3°F.

Bayfield County: May 11 to October 3 (145 days, 1 WNV)
Ashland County: May 13 to October 3 (144 days, 0 WNV)
Marinette County: May 14 to October 3 (142 days, 1 WNV)
Forest County: May 10 to September 29 (141 days, 0 WNV)

West Nile in Iron County

CDC ArboNET lists no human West Nile cases for Iron County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 3 of those years.

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