Mosquito season in Golden Valley County, MT: when it starts and ends

Mosquito months in Golden Valley County

In a normal year mosquito season in Golden Valley County, MT starts around May 7 and ends around October 3, about 21 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 Golden Valley County, and when

• Start tipping out standing water weekly by April 23.
• Book any yard treatment for early May, ahead of the July peak.
• Repellent can go away after October 3.
• No West Nile cases since 2016, so bites in Golden Valley County are a nuisance; check window screens.

Golden Valley County against the rest of MT

Golden Valley County has the 14th longest season of 56 MT counties, at 149 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 45.4°F.

• Cascade County: May 7 to October 4 (151 days, 12 WNV)
• Carbon County: May 7 to October 3 (149 days, 5 WNV)
• Carter County: May 6 to October 1 (148 days, 0 WNV)
• McCone County: May 6 to October 1 (148 days, 7 WNV)

West Nile in Golden Valley County

CDC ArboNET lists no human West Nile cases for Golden Valley County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 2 of those years.

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