Mosquito season in Lake County, MT: when it starts and ends
Mosquito months in Lake County
In a normal year mosquito season in Lake County, MT starts around May 4 and ends around October 4, about 22 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Lake County, and when
- Start tipping out standing water weekly by April 20.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 4.
- 2 West Nile cases since 2016 (last 2018): you should use repellent at dusk July, more so if over 60.
Lake County against the rest of MT
Lake County has the 10th longest season of 56 MT counties, at 153 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 46.1°F.
- Prairie County: May 2 to October 5 (155 days, 1 WNV)
- Sweet Grass County: May 3 to October 5 (155 days, 1 WNV)
- Fallon County: May 5 to October 3 (151 days, 0 WNV)
- Cascade County: May 7 to October 4 (151 days, 12 WNV)
West Nile in Lake County
From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Lake County (2 neuroinvasive) across 4 years. The worst was 2018 with 1; the latest was 2018.
More: how the dates are worked out · when mosquitoes go away for the winter.