Mosquito season in Summit County, CO: when it starts and ends
Mosquito months in Summit County
In a normal year mosquito season in Summit County, CO starts around June 20 and ends around August 28, about 10 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Summit County, and when
- Start tipping out standing water weekly by June 6.
- Book any yard treatment for mid June, ahead of the July peak.
- Repellent can go away after August 28.
- 2 West Nile cases since 2016 (last 2025): you should use repellent at dusk July, more so if over 60.
Summit County against the rest of CO
Summit County has the 64th longest season of 64 CO counties, at 69 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 33.7°F.
- Lake County: June 13 to September 3 (82 days, 0 WNV)
- San Juan County: June 22 to September 7 (77 days, 0 WNV)
West Nile in Summit County
From 1999 to 2025, CDC ArboNET counted 6 human West Nile cases in Summit County (1 neuroinvasive) across 4 years. The worst was 2003 with 3; the latest was 2025.
More: how the dates are worked out · when the season starts across the US.