Mosquito season in San Juan County, UT: when it starts and ends

Mosquito months in San Juan County

In a normal year mosquito season in San Juan County, UT starts around April 24 and ends around October 17, about 25 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 San Juan 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 17.
• 2 West Nile cases since 2016 (last 2017): you should use repellent at dusk July to August, more so if over 60.

San Juan County against the rest of UT

San Juan County has the 9th longest season of 29 UT counties, at 176 days against 210 in Salt Lake County and 82 in Summit County. Its mean temperature is 50.1°F.

• Washington County: April 24 to October 22 (181 days, 9 WNV)
• Uintah County: April 19 to October 13 (177 days, 6 WNV)
• Carbon County: April 24 to October 15 (174 days, 0 WNV)
• Cache County: April 27 to October 12 (168 days, 22 WNV)

West Nile in San Juan County

From 1999 to 2025, CDC ArboNET counted 5 human West Nile cases in San Juan County (3 neuroinvasive) across 3 years. The worst was 2017 with 2; the latest was 2017.

See how the dates are worked out, and when mosquitoes go away for the winter.