Mosquito season in Johnson County, WY: when it starts and ends
Mosquito months in Johnson County
In a normal year mosquito season in Johnson County, WY starts around May 11 and ends around September 30, about 20 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Johnson County, and when
- Start tipping out standing water weekly by April 27.
- Book any yard treatment for mid May, ahead of the July peak.
- Repellent can go away after September 30.
- No West Nile cases since 2016, so bites in Johnson County are a nuisance; check window screens.
Johnson County against the rest of WY
Johnson County has the 14th longest season of 23 WY counties, at 142 days against 163 in Big Horn County and 75 in Teton County. Its mean temperature is 45°F.
- Natrona County: May 11 to October 1 (143 days, 12 WNV)
- Washakie County: May 9 to September 28 (142 days, 3 WNV)
- Crook County: May 14 to October 1 (140 days, 1 WNV)
- Hot Springs County: May 14 to September 29 (138 days, 1 WNV)
West Nile in Johnson County
From 1999 to 2025, CDC ArboNET counted 11 human West Nile cases in Johnson County (5 neuroinvasive) across 4 years. The worst was 2003 with 8; the latest was 2015.
See how the dates are worked out, and when the season starts across the US.