Mosquito season in Fallon County, MT: when it starts and ends
Mosquito months in Fallon County
In a normal year mosquito season in Fallon County, MT starts around May 5 and ends around October 3, about 22 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Fallon County, and when
- Start tipping out standing water weekly by April 21.
- 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 Fallon County are a nuisance; check window screens.
Fallon County against the rest of MT
Fallon County has the 11th longest season of 56 MT counties, at 151 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 44°F.
- Sweet Grass County: May 3 to October 5 (155 days, 1 WNV)
- Lake County: May 4 to October 4 (153 days, 2 WNV)
- Cascade County: May 7 to October 4 (151 days, 12 WNV)
- Carbon County: May 7 to October 3 (149 days, 5 WNV)
West Nile in Fallon County
From 1999 to 2025, CDC ArboNET counted 8 human West Nile cases in Fallon County (5 neuroinvasive) across 2 years. The worst was 2003 with 6; the latest was 2007.
See how the dates are worked out, and when the season starts across the US.