Mosquito season in Grand County, UT: when it starts and ends
Mosquito months in Grand County
In a normal year mosquito season in Grand County, UT starts around April 8 and ends around October 26, about 29 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Grand County, and when
- Start tipping out standing water weekly by March 25.
- Book any yard treatment for early April, ahead of the July peak.
- Repellent can go away after October 26.
- 4 West Nile cases since 2016 (last 2019): you should use repellent at dusk June to August, more so if over 60.
Grand County against the rest of UT
Grand County has the 3rd longest season of 29 UT counties, at 201 days against 210 in Salt Lake County and 82 in Summit County. Its mean temperature is 54.7°F.
- Salt Lake County: April 2 to October 29 (210 days, 70 WNV)
- Wayne County: April 5 to October 24 (202 days, 0 WNV)
- Utah County: April 9 to October 25 (199 days, 28 WNV)
- Davis County: April 16 to October 20 (188 days, 36 WNV)
West Nile in Grand County
From 1999 to 2025, CDC ArboNET counted 6 human West Nile cases in Grand County (2 neuroinvasive) across 4 years. The worst was 2019 with 3; the latest was 2019.
Background: reading the West Nile counts; how the dates are worked out.