Mosquito season in Franklin County, WA: when it starts and ends
Mosquito months in Franklin County
In a normal year mosquito season in Franklin County, WA starts around April 10 and ends around October 18, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Franklin County, and when
- Start tipping out standing water weekly by March 27.
- Book any yard treatment for early April, ahead of the July peak.
- Repellent can go away after October 18.
- 1 West Nile case since 2016 (last 2021): you should use repellent at dusk July to August, more so if over 60.
Franklin County against the rest of WA
Franklin County has the 5th longest season of 39 WA counties, at 191 days against 205 in Walla Walla County and 132 in Asotin County. Its mean temperature is 51.8°F.
- Cowlitz County: April 11 to October 28 (200 days, 0 WNV)
- Kitsap County: April 15 to October 25 (193 days, 0 WNV)
- Yakima County: April 12 to October 17 (188 days, 4 WNV)
- Grant County: April 12 to October 16 (187 days, 0 WNV)
West Nile in Franklin County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Franklin County (2 neuroinvasive) across 2 years. The worst was 2015 with 2; the latest was 2021.
More: how the dates are worked out · when the season starts across the US.