Mosquito season in Ontario County, NY: when it starts and ends
Mosquito months in Ontario County
In a normal year mosquito season in Ontario County, NY starts around April 27 and ends around October 20, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Ontario County, and when
- Start tipping out standing water weekly by April 13.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 20.
- 1 West Nile case since 2016 (last 2025): you should use repellent at dusk July to July, more so if over 60.
Ontario County against the rest of NY
Ontario County has the 20th longest season of 62 NY counties, at 176 days against 218 in New York County and 125 in Franklin County. Its mean temperature is 48.5°F.
- Yates County: April 26 to October 19 (176 days, 0 WNV)
- Niagara County: April 27 to October 21 (176 days, 5 WNV)
- Saratoga County: April 23 to October 16 (175 days, 3 WNV)
- Genesee County: April 27 to October 17 (174 days, 1 WNV)
West Nile in Ontario County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Ontario County (1 neuroinvasive) across 1 year. The worst was 2025 with 1; the latest was 2025.
Background: when the season starts across the US; how the dates are worked out.