Mosquito season in Marin County, CA: when it starts and ends
Mosquito months in Marin County
In a normal year mosquito season in Marin County, CA starts around January 24 and ends around December 10, about 46 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Marin County, and when
- Start tipping out standing water weekly by January 10.
- Book any yard treatment for late January, ahead of the August peak.
- Repellent can go away after December 10.
- No West Nile cases since 2016, so bites in Marin County are a nuisance; check window screens.
Marin County against the rest of CA
Marin County has the 10th longest season of 58 CA counties, at 321 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 59.1°F.
- Santa Clara County: January 18 to December 11 (327 days, 16 WNV)
- Fresno County: January 22 to December 10 (321 days, 201 WNV)
- Kern County: January 25 to December 8 (316 days, 173 WNV)
- San Joaquin County: January 27 to December 7 (314 days, 86 WNV)
West Nile in Marin County
From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Marin County (3 neuroinvasive) across 3 years. The worst was 2013 with 2; the latest was 2015.
Background: when the season starts across the US; how the dates are worked out.