Mosquito season in Phillips County, MT: when it starts and ends
Mosquito months in Phillips County
In a normal year mosquito season in Phillips County, MT starts around April 30 and ends around October 6, about 23 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Phillips County, and when
- Start tipping out standing water weekly by April 16.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 6.
- 4 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Phillips County against the rest of MT
Phillips County has the 3rd longest season of 56 MT counties, at 159 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 44.6°F.
- Dawson County: April 28 to October 8 (163 days, 8 WNV)
- Treasure County: April 30 to October 7 (160 days, 0 WNV)
- Valley County: April 30 to October 5 (158 days, 12 WNV)
- Yellowstone County: April 30 to October 4 (157 days, 26 WNV)
West Nile in Phillips County
From 1999 to 2025, CDC ArboNET counted 24 human West Nile cases in Phillips County (3 neuroinvasive) across 5 years. The worst was 2007 with 16; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.