Mosquito season in Hamilton County, IN: when it starts and ends

Mosquito months in Hamilton County

In a normal year mosquito season in Hamilton County, IN starts around April 11 and ends around October 25, 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 Hamilton County, and when

• Start tipping out standing water weekly by March 28.
• Book any yard treatment for mid April, ahead of the July peak.
• Repellent can go away after October 25.
• 10 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check IN spray notices.

Hamilton County against the rest of IN

Hamilton County has the 45th longest season of 92 IN counties, at 197 days against 231 in Floyd County and 177 in Steuben County. Its mean temperature is 51.8°F.

• Clinton County: April 11 to October 26 (198 days, 1 WNV)
• Hancock County: April 11 to October 25 (198 days, 2 WNV)
• Rush County: April 11 to October 25 (197 days, 0 WNV)
• Blackford County: April 12 to October 26 (196 days, 0 WNV)

West Nile in Hamilton County

From 1999 to 2025, CDC ArboNET counted 21 human West Nile cases in Hamilton County (17 neuroinvasive) across 10 years. The worst was 2018 with 5; the latest was 2025.

More: how the dates are worked out · reading the West Nile counts.