Mosquito season in Morgan County, IL: when it starts and ends

Mosquito months in Morgan County

In a normal year mosquito season in Morgan County, IL starts around April 8 and ends around October 27, about 29 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 Morgan 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.
• 1 West Nile case since 2016 (last 2025): you should use repellent at dusk June to August, more so if over 60.

Morgan County against the rest of IL

Morgan County has the 53rd longest season of 102 IL counties, at 202 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 52.7°F.

• Vermilion County: April 8 to October 28 (203 days, 1 WNV)
• Brown County: April 8 to October 27 (202 days, 0 WNV)
• Cass County: April 8 to October 27 (201 days, 0 WNV)
• Douglas County: April 8 to October 27 (201 days, 1 WNV)

West Nile in Morgan County

From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Morgan County (3 neuroinvasive) across 4 years. The worst was 2025 with 1; the latest was 2025.

See how the dates are worked out, and when the season starts across the US.