Mosquito season in Judith Basin County, MT: when it starts and ends

Mosquito months in Judith Basin County

In a normal year mosquito season in Judith Basin County, MT starts around May 25 and ends around September 18, about 17 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Judith Basin County, and when

• Start tipping out standing water weekly by May 11.
• Book any yard treatment for late May, ahead of the July peak.
• Repellent can go away after September 18.
• No West Nile cases since 2016, so bites in Judith Basin County are a nuisance; check window screens.

Judith Basin County against the rest of MT

Judith Basin County has the 49th longest season of 56 MT counties, at 116 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 42.5°F.

• Deer Lodge County: May 25 to September 23 (121 days, 0 WNV)
• Daniels County: May 19 to September 16 (120 days, 0 WNV)
• Silver Bow County: May 27 to September 17 (113 days, 0 WNV)
• Glacier County: May 30 to September 20 (113 days, 0 WNV)

West Nile in Judith Basin County

CDC ArboNET lists no human West Nile cases for Judith Basin County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 2 of those years.

Background: when the season starts across the US; how the dates are worked out.