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

Mosquito months in Franklin County

In a normal year mosquito season in Franklin County, ID starts around April 30 and ends around October 10, about 23 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 Franklin County, and when

• Start tipping out standing water weekly by April 16.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 10.
• 2 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to July, more so if over 60.

Franklin County against the rest of ID

Franklin County has the 11th longest season of 44 ID counties, at 163 days against 194 in Canyon County and 85 in Fremont County. Its mean temperature is 46.9°F.

• Gem County: April 28 to October 12 (167 days, 7 WNV)
• Bingham County: April 28 to October 9 (164 days, 2 WNV)
• Washington County: April 28 to October 7 (162 days, 19 WNV)
• Minidoka County: May 2 to October 11 (162 days, 0 WNV)

West Nile in Franklin County

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

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