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

Mosquito months in Franklin County

In a normal year mosquito season in Franklin County, OH starts around April 8 and ends around October 27, about 29 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 Franklin County, and when

• Start tipping out standing water weekly by March 25.
• Book any yard treatment for early April, ahead of the July peak.
• Repellent can go away after October 27.
• 18 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check OH spray notices.

Franklin County against the rest of OH

Franklin County has the 13th longest season of 88 OH counties, at 202 days against 209 in Gallia County and 177 in Ashtabula County. Its mean temperature is 52.9°F.

• Miami County: April 8 to October 28 (203 days, 1 WNV)
• Butler County: April 8 to October 27 (202 days, 3 WNV)
• Delaware County: April 9 to October 28 (202 days, 0 WNV)
• Pike County: April 9 to October 28 (202 days, 0 WNV)

West Nile in Franklin County

From 1999 to 2025, CDC ArboNET counted 50 human West Nile cases in Franklin County (34 neuroinvasive) across 16 years. The worst was 2002 with 9; the latest was 2025.

See how the dates are worked out, and reading the West Nile counts.