Mosquito season in Madison County, MT: when it starts and ends
Mosquito months in Madison County
In a normal year mosquito season in Madison County, MT starts around May 22 and ends around September 26, about 18 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Madison County, and when
- Start tipping out standing water weekly by May 8.
- Book any yard treatment for late May, ahead of the July peak.
- Repellent can go away after September 26.
- 1 West Nile case since 2016 (last 2017): you should use repellent at dusk July, more so if over 60.
Madison County against the rest of MT
Madison County has the 41st longest season of 56 MT counties, at 127 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 42°F.
- Sheridan County: May 15 to September 22 (130 days, 2 WNV)
- Lewis and Clark County: May 20 to September 26 (128 days, 6 WNV)
- Meagher County: May 22 to September 25 (126 days, 0 WNV)
- Ravalli County: May 22 to September 24 (125 days, 1 WNV)
West Nile in Madison County
From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Madison County (0 neuroinvasive) across 2 years. The worst was 2017 with 1; the latest was 2017.
See how the dates are worked out, and when mosquitoes go away for the winter.