Mosquito season in Ada County, ID: when it starts and ends
Mosquito months in Ada County
In a normal year mosquito season in Ada County, ID starts around April 12 and ends around October 23, about 28 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Ada County, and when
- Start tipping out standing water weekly by March 29.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 23.
- 36 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to August, and check ID spray notices.
Ada County against the rest of ID
Ada County has the 3rd longest season of 44 ID counties, at 193 days against 194 in Canyon County and 85 in Fremont County. Its mean temperature is 52.8°F.
- Canyon County: April 9 to October 21 (194 days, 20 WNV)
- Payette County: April 9 to October 19 (194 days, 6 WNV)
- Gooding County: April 19 to October 15 (179 days, 9 WNV)
- Nez Perce County: April 22 to October 14 (175 days, 0 WNV)
West Nile in Ada County
From 1999 to 2025, CDC ArboNET counted 339 human West Nile cases in Ada County (52 neuroinvasive) across 20 years. The worst was 2006 with 252; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.