Mosquito season in Dawson County, MT: when it starts and ends
Mosquito months in Dawson County
In a normal year mosquito season in Dawson County, MT starts around April 28 and ends around October 8, about 23 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Dawson County, and when
- Start tipping out standing water weekly by April 14.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 8.
- 8 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Dawson County against the rest of MT
Dawson County has the 1st longest season of 56 MT counties, at 163 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 45.7°F.
- Treasure County: April 30 to October 7 (160 days, 0 WNV)
- Phillips County: April 30 to October 6 (159 days, 4 WNV)
West Nile in Dawson County
From 1999 to 2025, CDC ArboNET counted 23 human West Nile cases in Dawson County (6 neuroinvasive) across 6 years. The worst was 2003 with 9; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.