Mosquito season in Sweetwater County, WY: when it starts and ends

Mosquito months in Sweetwater County

In a normal year mosquito season in Sweetwater County, WY starts around May 12 and ends around October 2, about 21 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 Sweetwater County, and when

• Start tipping out standing water weekly by April 28.
• Book any yard treatment for mid May, ahead of the July peak.
• Repellent can go away after October 2.
• No West Nile cases since 2016, so bites in Sweetwater County are a nuisance; check window screens.

Sweetwater County against the rest of WY

Sweetwater County has the 11th longest season of 23 WY counties, at 144 days against 163 in Big Horn County and 75 in Teton County. Its mean temperature is 43.8°F.

• Laramie County: May 9 to October 1 (145 days, 11 WNV)
• Platte County: May 9 to October 1 (145 days, 6 WNV)
• Natrona County: May 11 to October 1 (143 days, 12 WNV)
• Washakie County: May 9 to September 28 (142 days, 3 WNV)

West Nile in Sweetwater County

From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Sweetwater County (0 neuroinvasive) across 1 year. The worst was 2007 with 1; the latest was 2007.

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