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

Mosquito months in Union County

In a normal year mosquito season in Union County, OH starts around April 10 and ends around October 26, about 28 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 Union 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 26.
• No West Nile cases since 2016, so bites in Union County are a nuisance; check window screens.

Union County against the rest of OH

Union County has the 19th longest season of 88 OH counties, at 198 days against 209 in Gallia County and 177 in Ashtabula County. Its mean temperature is 52.1°F.

• Hancock County: April 12 to October 27 (199 days, 4 WNV)
• Jackson County: April 9 to October 24 (198 days, 0 WNV)
• Athens County: April 11 to October 26 (198 days, 1 WNV)
• Darke County: April 11 to October 25 (198 days, 1 WNV)

West Nile in Union County

From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Union County (4 neuroinvasive) across 3 years. The worst was 2002 with 2; the latest was 2013.

See how the dates are worked out, and when mosquitoes go away for the winter.