Illinois frost dates

Across Illinois, the average last spring frost is around April 20 and the average first fall frost around October 14 — roughly 177 frost-free days. USDA zones 5a, 5b, 6a, 6b, 7a.

Risk you accept	Last spring frost by	First fall frost by
Cautious (~10%)	May 4	September 30
Average (~50%)	April 20	October 14
Gambler (~90%)	April 6	October 28

→ Turn these into sowing dates with the Illinois planting calendar, or look up an exact ZIP code.

Statewide average from NOAA/NCEI freeze normals. Cautious/gambler dates are about two weeks either side of the average.