Mosquito season in Carbon County, MT: when it starts and ends
Mosquito months in Carbon County
In a normal year mosquito season in Carbon County, MT starts around May 7 and ends around October 3, about 21 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Carbon County, and when
- Start tipping out standing water weekly by April 23.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 3.
- 5 West Nile cases since 2016 (last 2025): you should use repellent at dusk July, more so if over 60.
Carbon County against the rest of MT
Carbon County has the 13th longest season of 56 MT counties, at 149 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 44.8°F.
- Fallon County: May 5 to October 3 (151 days, 0 WNV)
- Cascade County: May 7 to October 4 (151 days, 12 WNV)
- Golden Valley County: May 7 to October 3 (149 days, 0 WNV)
- Carter County: May 6 to October 1 (148 days, 0 WNV)
West Nile in Carbon County
From 1999 to 2025, CDC ArboNET counted 8 human West Nile cases in Carbon County (7 neuroinvasive) across 6 years. The worst was 2025 with 3; the latest was 2025.
See how the dates are worked out, and reading the West Nile counts.