Mosquito season in Trinity County, CA: when it starts and ends
Mosquito months in Trinity County
In a normal year mosquito season in Trinity County, CA starts around April 11 and ends around October 29, about 29 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Trinity County, and when
- Start tipping out standing water weekly by March 28.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 29.
- No West Nile cases since 2016, so bites in Trinity County are a nuisance; check window screens.
Trinity County against the rest of CA
Trinity County has the 48th longest season of 58 CA counties, at 201 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 55.9°F.
- Mendocino County: March 31 to October 30 (213 days, 0 WNV)
- Del Norte County: April 5 to November 2 (211 days, 0 WNV)
- El Dorado County: April 15 to October 29 (197 days, 6 WNV)
- Siskiyou County: April 16 to October 25 (192 days, 1 WNV)
West Nile in Trinity County
CDC ArboNET lists no human West Nile cases for Trinity County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 6 of those years.
See how the dates are worked out, and when the season starts across the US.