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

Mosquito months in Adams County

In a normal year mosquito season in Adams County, IL starts around April 6 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 Adams County, and when

• Start tipping out standing water weekly by March 23.
• Book any yard treatment for early April, ahead of the July peak.
• Repellent can go away after October 27.
• 4 West Nile cases since 2016 (last 2025): you should use repellent at dusk June to August, more so if over 60.

Adams County against the rest of IL

Adams County has the 47th longest season of 102 IL counties, at 204 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 52.9°F.

• Macon County: April 6 to October 28 (205 days, 4 WNV)
• Moultrie County: April 6 to October 28 (205 days, 0 WNV)
• Greene County: April 7 to October 28 (204 days, 0 WNV)
• Sangamon County: April 7 to October 28 (204 days, 8 WNV)

West Nile in Adams County

From 1999 to 2025, CDC ArboNET counted 9 human West Nile cases in Adams County (4 neuroinvasive) across 8 years. The worst was 2025 with 2; the latest was 2025.

See how the dates are worked out, and reading the West Nile counts.