Mosquito season in Marion County, IN: when it starts and ends
Mosquito months in Marion County
In a normal year mosquito season in Marion County, IN starts around April 8 and ends around October 27, about 29 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Marion 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 IN spray notices.
Marion County against the rest of IN
Marion County has the 37th longest season of 92 IN counties, at 202 days against 231 in Floyd County and 177 in Steuben County. Its mean temperature is 52.5°F.
- Shelby County: April 8 to October 28 (203 days, 1 WNV)
- Ohio County: April 11 to October 31 (203 days, 1 WNV)
- Hendricks County: April 9 to October 27 (201 days, 1 WNV)
- Madison County: April 9 to October 27 (201 days, 2 WNV)
West Nile in Marion County
From 1999 to 2025, CDC ArboNET counted 97 human West Nile cases in Marion County (72 neuroinvasive) across 22 years. The worst was 2002 with 41; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.