Mackinaw, IL 61755 Frost Dates
Frost dates for Mackinaw, IL, ZIP 61755
Typically, the last spring freeze lands around 04/21, roughly 236 days out. The first fall frost typically arrives around 10/17, about 178 frost-free days later.
Zone 6a (-10 to -5°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for Mackinaw, not a forecast for this year.
What to do before the first frost
Zone 6a around Mackinaw has about 7 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
Why 04/21 isn't a guarantee
04/21 is the middle of 30 years of NOAA records, not a promise. Plant by 04/07 and you're betting against frost in roughly 9 years out of 10. 05/07 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Mackinaw compares
At roughly 178 frost-free days, Mackinaw places 25,761 of 40,283 ZIP codes in this dataset. Within IL, it ranks 1,086 of 1,548.
Learn more
zone vs. frost date explains why Zone 6a and Mackinaw's frost date answer different questions, and the frost range explains how to read the range around Mackinaw's dates instead of trusting one.