Mosquito season in Washington County, OH: when it starts and ends
Mosquito months in Washington County
In a normal year mosquito season in Washington County, OH starts around April 6 and ends around October 29, about 30 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Washington County, and when
- Start tipping out standing water weekly by March 23.
- Book any yard treatment for early April, ahead of the July peak.
- Repellent can go away after October 29.
- No West Nile cases since 2016, so bites in Washington County are a nuisance; check window screens.
Washington County against the rest of OH
Washington County has the 5th longest season of 88 OH counties, at 207 days against 209 in Gallia County and 177 in Ashtabula County. Its mean temperature is 53.8°F.
- Greene County: April 5 to October 30 (208 days, 1 WNV)
- Hamilton County: April 5 to October 30 (208 days, 13 WNV)
- Scioto County: April 7 to October 31 (207 days, 0 WNV)
- Montgomery County: April 6 to October 29 (206 days, 14 WNV)
West Nile in Washington County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Washington County (0 neuroinvasive) across 1 year. The worst was 2003 with 1; the latest was 2003.
See how the dates are worked out, and when the season starts across the US.