Mosquito season in Mercer County, OH: when it starts and ends
Mosquito months in Mercer County
In a normal year mosquito season in Mercer County, OH starts around April 15 and ends around October 25, about 28 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Mercer County, and when
- Start tipping out standing water weekly by April 1.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 25.
- 2 West Nile cases since 2016 (last 2023): you should use repellent at dusk June to August, more so if over 60.
Mercer County against the rest of OH
Mercer County has the 37th longest season of 88 OH counties, at 193 days against 209 in Gallia County and 177 in Ashtabula County. Its mean temperature is 51.3°F.
- Morgan County: April 15 to October 26 (194 days, 0 WNV)
- Allen County: April 15 to October 25 (193 days, 1 WNV)
- Putnam County: April 15 to October 24 (193 days, 1 WNV)
- Lorain County: April 16 to October 26 (193 days, 3 WNV)
West Nile in Mercer County
From 1999 to 2025, CDC ArboNET counted 10 human West Nile cases in Mercer County (7 neuroinvasive) across 5 years. The worst was 2002 with 4; the latest was 2023.
More: how the dates are worked out · when the season starts across the US.