Mosquito season in Hardin County, IA: when it starts and ends

Mosquito months in Hardin County

In a normal year mosquito season in Hardin County, IA starts around April 23 and ends around October 15, about 25 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 Hardin County, and when

• Start tipping out standing water weekly by April 9.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 15.
• 2 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.

Hardin County against the rest of IA

Hardin County has the 71st longest season of 99 IA counties, at 175 days against 198 in Des Moines County and 160 in Worth County. Its mean temperature is 46.8°F.

• Plymouth County: April 22 to October 14 (175 days, 10 WNV)
• Guthrie County: April 23 to October 15 (175 days, 1 WNV)
• Humboldt County: April 23 to October 15 (175 days, 3 WNV)
• Floyd County: April 22 to October 14 (174 days, 1 WNV)

West Nile in Hardin County

From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Hardin County (4 neuroinvasive) across 3 years. The worst was 2025 with 2; the latest was 2025.

See how the dates are worked out, and when mosquitoes go away for the winter.