Mosquito season in Hill County, MT: when it starts and ends
Mosquito months in Hill County
In a normal year mosquito season in Hill County, MT starts around May 12 and ends around September 26, about 20 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Hill County, and when
- Start tipping out standing water weekly by April 28.
- Book any yard treatment for mid May, ahead of the July peak.
- Repellent can go away after September 26.
- 2 West Nile cases since 2016 (last 2018): you should use repellent at dusk July, more so if over 60.
Hill County against the rest of MT
Hill County has the 33rd longest season of 56 MT counties, at 137 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 42.5°F.
- Powder River County: May 14 to September 29 (138 days, 1 WNV)
- Custer County: May 11 to September 25 (137 days, 6 WNV)
- Stillwater County: May 13 to September 26 (136 days, 1 WNV)
- Wheatland County: May 16 to September 27 (134 days, 0 WNV)
West Nile in Hill County
From 1999 to 2025, CDC ArboNET counted 30 human West Nile cases in Hill County (8 neuroinvasive) across 6 years. The worst was 2007 with 13; the latest was 2018.
See how the dates are worked out, and when mosquitoes go away for the winter.