Mosquito season in Marion County, OH: when it starts and ends
Mosquito months in Marion County
In a normal year mosquito season in Marion County, OH starts around April 16 and ends around October 23, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Marion County, and when
- Start tipping out standing water weekly by April 2.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 23.
- 3 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Marion County against the rest of OH
Marion County has the 54th longest season of 88 OH counties, at 190 days against 209 in Gallia County and 177 in Ashtabula County. Its mean temperature is 50.6°F.
- Ottawa County: April 17 to October 26 (191 days, 1 WNV)
- Logan County: April 16 to October 23 (190 days, 2 WNV)
- Richland County: April 16 to October 23 (190 days, 2 WNV)
- Seneca County: April 17 to October 24 (190 days, 0 WNV)
West Nile in Marion County
From 1999 to 2025, CDC ArboNET counted 7 human West Nile cases in Marion County (4 neuroinvasive) across 4 years. The worst was 2002 with 3; the latest was 2025.
Background: when the season starts across the US; how the dates are worked out.