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

Mosquito months in San Miguel County

In a normal year mosquito season in San Miguel County, CO starts around June 15 and ends around September 16, about 13 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 Miguel County, and when

• Start tipping out standing water weekly by June 1.
• Book any yard treatment for mid June, ahead of the July peak.
• Repellent can go away after September 16.
• 2 West Nile cases since 2016 (last 2019): you should use repellent at dusk July, more so if over 60.

San Miguel County against the rest of CO

San Miguel County has the 56th longest season of 64 CO counties, at 93 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 43.1°F.

• Mineral County: June 10 to September 16 (98 days, 0 WNV)
• Hinsdale County: June 8 to September 12 (96 days, 0 WNV)
• Jackson County: June 8 to September 8 (92 days, 0 WNV)
• Chaffee County: June 9 to September 8 (91 days, 11 WNV)

West Nile in San Miguel County

From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in San Miguel County (2 neuroinvasive) across 2 years. The worst was 2019 with 1; the latest was 2019.

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