Illinois · zones 5b–6b
When to plant sweet corn in Illinois.
Sow between Apr 27 to Jul 27 in a typical year, keyed to Illinois's median last frost around Apr 20. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Sweet Corn dates for a typical Illinois season.
Direct sow
Apr 27 to Jul 27
Keyed to the ~Apr 20 last frost. Sow 1.5" deep, 12" apart.
Harvest
~75 days later
~1 lb per plant over ~1 weeks.
Illinois spans more than one climate: Zone 6 is the most common zone, but the state runs 5b to 6b. That's why the planner works from your ZIP code's frost dates, not your zone — mountain and coastal gardens in the same state can be three weeks apart.