Mosquito season in Lemhi County, ID: when it starts and ends

Mosquito months in Lemhi County

In a normal year mosquito season in Lemhi County, ID starts around June 10 and ends around September 4, about 12 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 Lemhi County, and when

• Start tipping out standing water weekly by May 27.
• Book any yard treatment for early June, ahead of the July peak.
• Repellent can go away after September 4.
• 2 West Nile cases since 2016 (last 2021): you should use repellent at dusk July, more so if over 60.

Lemhi County against the rest of ID

Lemhi County has the 43rd longest season of 44 ID counties, at 86 days against 194 in Canyon County and 85 in Fremont County. Its mean temperature is 39°F.

• Blaine County: June 7 to September 21 (106 days, 0 WNV)
• Adams County: June 1 to September 9 (100 days, 2 WNV)
• Fremont County: June 9 to September 2 (85 days, 0 WNV)

West Nile in Lemhi County

From 1999 to 2025, CDC ArboNET counted 11 human West Nile cases in Lemhi County (3 neuroinvasive) across 5 years. The worst was 2007 with 6; the latest was 2021.

See how the dates are worked out, and when mosquitoes go away for the winter.