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

Mosquito months in San Juan County

In a normal year mosquito season in San Juan County, CO starts around June 22 and ends around September 7, about 11 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 June 8.
• Book any yard treatment for late June, ahead of the July peak.
• Repellent can go away after September 7.
• No West Nile cases since 2016, so bites in San Juan County are a nuisance; check window screens.

San Juan County against the rest of CO

San Juan County has the 63rd longest season of 64 CO counties, at 77 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 35.2°F.

• Park County: June 15 to September 8 (85 days, 0 WNV)
• Lake County: June 13 to September 3 (82 days, 0 WNV)
• Summit County: June 20 to August 28 (69 days, 2 WNV)

West Nile in San Juan County

CDC ArboNET lists no human West Nile cases for San Juan County from 1999 to 2025.

Background: when the season starts across the US; how the dates are worked out.