Mosquito season in Defiance County, OH: when it starts and ends

Mosquito months in Defiance County

In a normal year mosquito season in Defiance County, OH starts around April 17 and ends around October 21, about 27 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Defiance County, and when

• Start tipping out standing water weekly by April 3.
• Book any yard treatment for mid April, ahead of the July peak.
• Repellent can go away after October 21.
• 2 West Nile cases since 2016 (last 2018): you should use repellent at dusk July to August, more so if over 60.

Defiance County against the rest of OH

Defiance County has the 66th longest season of 88 OH counties, at 187 days against 209 in Gallia County and 177 in Ashtabula County. Its mean temperature is 50.1°F.

• Hocking County: April 19 to October 24 (188 days, 0 WNV)
• Licking County: April 19 to October 24 (188 days, 1 WNV)
• Wyandot County: April 18 to October 22 (187 days, 2 WNV)
• Huron County: April 19 to October 23 (187 days, 1 WNV)

West Nile in Defiance County

From 1999 to 2025, CDC ArboNET counted 11 human West Nile cases in Defiance County (4 neuroinvasive) across 5 years. The worst was 2002 with 6; the latest was 2018.

More: how the dates are worked out · when mosquitoes go away for the winter.