Mosquito season in Routt County, CO: when it starts and ends
Mosquito months in Routt County
In a normal year mosquito season in Routt County, CO starts around May 20 and ends around September 23, about 18 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Routt County, and when
- Start tipping out standing water weekly by May 6.
- Book any yard treatment for mid May, ahead of the July peak.
- Repellent can go away after September 23.
- No West Nile cases since 2016, so bites in Routt County are a nuisance; check window screens.
Routt County against the rest of CO
Routt County has the 42nd longest season of 64 CO counties, at 126 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 42.3°F.
- Rio Grande County: May 19 to September 26 (130 days, 1 WNV)
- Archuleta County: May 23 to September 30 (130 days, 4 WNV)
- Larimer County: May 23 to September 26 (126 days, 225 WNV)
- Pitkin County: May 23 to September 25 (126 days, 1 WNV)
West Nile in Routt County
CDC ArboNET lists no human West Nile cases for Routt County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 2 of those years.
See how the dates are worked out, and when mosquitoes go away for the winter.