Mosquito season in Cascade County, MT: when it starts and ends
Mosquito months in Cascade County
In a normal year mosquito season in Cascade County, MT starts around May 7 and ends around October 4, about 22 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Cascade 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 4.
- 12 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July, and check MT spray notices.
Cascade County against the rest of MT
Cascade County has the 12th longest season of 56 MT counties, at 151 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 45.4°F.
- Lake County: May 4 to October 4 (153 days, 2 WNV)
- Fallon County: May 5 to October 3 (151 days, 0 WNV)
- Carbon County: May 7 to October 3 (149 days, 5 WNV)
- Golden Valley County: May 7 to October 3 (149 days, 0 WNV)
West Nile in Cascade County
From 1999 to 2025, CDC ArboNET counted 41 human West Nile cases in Cascade County (16 neuroinvasive) across 7 years. The worst was 2018 with 12; the latest was 2018.
See how the dates are worked out, and reading the West Nile counts.