Mosquito season in Liberty County, MT: when it starts and ends
Mosquito months in Liberty County
In a normal year mosquito season in Liberty County, MT starts around May 11 and ends around September 26, about 20 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Liberty 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 26.
- No West Nile cases since 2016, so bites in Liberty County are a nuisance; check window screens.
Liberty County against the rest of MT
Liberty County has the 29th longest season of 56 MT counties, at 138 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 41.5°F.
- Park County: May 14 to October 1 (140 days, 1 WNV)
- Teton County: May 14 to September 29 (139 days, 1 WNV)
- Toole County: May 11 to September 26 (138 days, 4 WNV)
- Powder River County: May 14 to September 29 (138 days, 1 WNV)
West Nile in Liberty County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Liberty County (0 neuroinvasive) across 3 years. The worst was 2013 with 1; the latest was 2013.
More: how the dates are worked out · when mosquitoes go away for the winter.