Mosquito season in Sheridan County, WY: when it starts and ends
Mosquito months in Sheridan County
In a normal year mosquito season in Sheridan County, WY starts around May 8 and ends around October 5, about 21 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Sheridan County, and when
- Start tipping out standing water weekly by April 24.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 5.
- 3 West Nile cases since 2016 (last 2023): you should use repellent at dusk July to July, more so if over 60.
Sheridan County against the rest of WY
Sheridan County has the 5th longest season of 23 WY counties, at 150 days against 163 in Big Horn County and 75 in Teton County. Its mean temperature is 45.3°F.
- Fremont County: May 4 to October 4 (153 days, 12 WNV)
- Niobrara County: May 5 to October 5 (153 days, 0 WNV)
- Converse County: May 8 to October 1 (146 days, 1 WNV)
- Weston County: May 9 to October 2 (146 days, 0 WNV)
West Nile in Sheridan County
From 1999 to 2025, CDC ArboNET counted 26 human West Nile cases in Sheridan County (8 neuroinvasive) across 7 years. The worst was 2003 with 11; the latest was 2023.
Background: when mosquitoes go away for the winter; how the dates are worked out.