Frost dates in Illinois

Across Illinois's 170 NOAA stations with a frost every year, the typical last spring frost ranges from April 2 at Mount Carmel (430 feet above sea level) to May 2 at Mount Carroll (640 feet above sea level). The middle station's date is April 18.

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Last frost across Illinois

The frost-free season runs from 154 days at Mount Carroll to 216 days at Grand Chain Dam 53.

The station with the latest frost is about 250 miles farther north than the one with the earliest.

These are typical dates: in half of springs the last frost comes later. Each place's page, and each ZIP code lookup, also gives the late-year date, after which only 1 spring in 10 has a frost. That's the safer date for tender plants.

Frost dates for Illinois's larger places

Typical (1-in-2) dates. Each place's page has the early and late years, a planting calendar and a printable planner. Zones are for the ZIP code nearest each place's center.

Hardiness zones in Illinois

Illinois's 1,545 ZIP codes in the USDA list fall in zones 5a to 7a: 5a (2 percent), 5b (29 percent), 6a (42 percent), 6b (17 percent) and 7a (11 percent). Compared with the 2012 map, 55 percent of them moved to a warmer half zone (6 by a full zone or more) and 45 percent stayed the same.

A hardiness zone is about the coldest night of winter, which decides which shrubs, trees and perennials survive. Frost dates are about spring and fall, which decide when to plant. You need both. Read more about what the zones mean and what changed in 2023.

Every NOAA station in Illinois

All 170 stations in Illinois with frost statistics in NOAA's 1991 to 2020 normals, from A to Z. Station names are usually a town, an airport, or a distance and direction from a town. Find one near you and at a similar elevation.

Typical (1-in-2) dates at 32°F. For the early and late years, and a planting calendar built from your own dates, look up your ZIP code.