Mosquito season in Washington County, UT: when it starts and ends
Mosquito months in Washington County
In a normal year mosquito season in Washington County, UT starts around April 24 and ends around October 22, about 26 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Washington County, and when
- Start tipping out standing water weekly by April 10.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 22.
- 9 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Washington County against the rest of UT
Washington County has the 7th longest season of 29 UT counties, at 181 days against 210 in Salt Lake County and 82 in Summit County. Its mean temperature is 52.6°F.
- Davis County: April 16 to October 20 (188 days, 36 WNV)
- Garfield County: April 22 to October 20 (181 days, 0 WNV)
- Uintah County: April 19 to October 13 (177 days, 6 WNV)
- San Juan County: April 24 to October 17 (176 days, 2 WNV)
West Nile in Washington County
From 1999 to 2025, CDC ArboNET counted 27 human West Nile cases in Washington County (12 neuroinvasive) across 10 years. The worst was 2005 with 6; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.