What Planting Zones Are in Illinois?
Illinois spans USDA hardiness zones 5a to 7a, where the average coldest winter night ranges from −20 °F to 5 °F (−28.9 °C to −15 °C). Zone 6a covers the most ZIP codes, 42%, and zones 5b to 7a together cover 98% of the state.
- Zone 5a2% · 28 ZIPs
- Zone 5b29% · 447 ZIPs
- Zone 6a42% · 646 ZIPs
- Zone 6b17% · 260 ZIPs
- Zone 7a11% · 164 ZIPs
Bars show each zone's share of the 1,545 Illinois ZIP codes in the official 2023 USDA ZIP code table; select a zone for its temperatures and hardy plants.
What Hardiness Zone Are Illinois Cities In?
Chicago is in zone 6a, Aurora is in zone 5b, Naperville is in zone 5b and Joliet is in zone 5b. The table lists the zone, winter low and average frost dates for 19 Illinois cities, using the ZIP code nearest each city center.
| City | ZIP | Zone | Winter low | Last frost | First frost |
|---|---|---|---|---|---|
| Chicago | 60608 | 6a | −10 °F to −5 °F | Apr 10 | Nov 5 |
| Aurora | 60505 | 5b | −15 °F to −10 °F | Apr 19 | Oct 23 |
| Naperville | 60540 | 5b | −15 °F to −10 °F | Apr 28 | Oct 16 |
| Joliet | 60431 | 5b | −15 °F to −10 °F | Apr 19 | Oct 25 |
| Rockford | 61104 | 5b | −15 °F to −10 °F | Apr 24 | Oct 17 |
| Elgin | 60123 | 5b | −15 °F to −10 °F | Apr 26 | Oct 18 |
| Springfield | 62701 | 6a | −10 °F to −5 °F | Apr 15 | Oct 22 |
| Peoria | 61614 | 6a | −10 °F to −5 °F | Apr 16 | Oct 23 |
| Champaign | 61821 | 6a | −10 °F to −5 °F | Apr 15 | Oct 24 |
| Waukegan | 60085 | 6a | −10 °F to −5 °F | Apr 30 | Oct 19 |
| Bloomington | 61701 | 6a | −10 °F to −5 °F | Apr 21 | Oct 20 |
| Arlington Heights | 60004 | 6a | −10 °F to −5 °F | Apr 19 | Oct 26 |
| Decatur | 62523 | 6a | −10 °F to −5 °F | Apr 14 | Oct 24 |
| Orland Park | 60467 | 6a | −10 °F to −5 °F | Apr 19 | Oct 22 |
| Moline | 61265 | 5b | −15 °F to −10 °F | Apr 24 | Oct 18 |
| Belleville | 62226 | 7a | 0 °F to 5 °F | Apr 12 | Oct 20 |
| DeKalb | 60115 | 5b | −15 °F to −10 °F | Apr 24 | Oct 18 |
| Quincy | 62301 | 6a | −10 °F to −5 °F | Apr 8 | Oct 30 |
| Godfrey | 62035 | 6b | −5 °F to 0 °F | Apr 4 | Nov 5 |
Zone: 2023 USDA ZIP code table for the ZIP code nearest each city's Census center point. Frost dates: 50% (median) dates from the nearest NOAA station, 1991–2020 normals. Cities: the largest Illinois places by 2024 Census population estimates, spread across the state, plus the largest place in each common zone. Large cities can span two half zones.
Which Parts of Illinois Are in Each Zone?
Zone 5a, the coldest Illinois zone, covers 2% of ZIP codes around Freeport, Galena and Savanna. Zone 7a, the warmest, covers 11% around Belleville, O'Fallon and Granite City. The table lists the largest places in every zone.
| Zone | Avg. coldest night | Share of ZIPs | Largest places in this zone |
|---|---|---|---|
| Zone 5a | −20 °F to −15 °F | 2% (28) | Freeport, Galena, Savanna, Lena |
| Zone 5b | −15 °F to −10 °F | 29% (447) | Aurora, Naperville, Joliet, Rockford |
| Zone 6a | −10 °F to −5 °F | 42% (646) | Chicago, Springfield, Peoria, Champaign |
| Zone 6b | −5 °F to 0 °F | 17% (260) | Godfrey, Mount Vernon, Effingham, Centralia |
| Zone 7a | 0 °F to 5 °F | 11% (164) | Belleville, O'Fallon, Granite City, Edwardsville |
Places: incorporated places with 1,000+ residents, assigned the zone of the ZIP code nearest their Census center point.
What Do the Hardiness Zones Mean for Illinois Gardeners?
A Illinois gardener in zone 7a sees winter lows about 20 °F milder than one in zone 5a, so a shrub or perennial that thrives in one part of the state can die in another. Choose plants rated to your own ZIP code's zone or colder.
Hardiness zones follow latitude, elevation and large bodies of water rather than state lines. Higher ground and inland valleys that trap cold air usually sit in colder half zones, while cities, coasts and large lakes moderate winter lows. Within Illinois, a plant labelled “zones 5–7” survives winter in at least 98% of ZIP codes, but plants at the edge of their range benefit from mulch and a sheltered spot. Enter a ZIP code in the USDA hardiness zone finder by ZIP code to check your exact half zone before buying perennials.
A zone describes winter cold only. Summer heat, humidity, rainfall and soil decide whether a cold-hardy plant thrives, and planting dates for vegetables follow frost dates, not zones: two Illinois towns in the same zone can have last frosts weeks apart.
What Plants Grow Well Across Illinois?
199 plants in PlantoScan's catalogue are hardy in every zone from 5b to 7a, the zones that cover 98% of Illinois ZIP codes. Popular examples include hydrangea, peony and daisy.
Hydrangea
Hydrangea macrophylla
Zone 5 – 9
AI generated
Peony
Paeonia lactiflora
Zone 3 – 8
AI generated
- DaisyBellis perennisPlantoScan
Daisy
Bellis perennis
Zone 4a – 8b
Chrysanthemum
Chrysanthemum morifolium
Zone 5a – 9b
PlantoscanAI generated
Poppy
Papaver somniferum
Zone 3a – 9b
AI generated
Carnation
Dianthus caryophyllus
Zone 5a – 9b
AI generated
Daffodil
Narcissus poeticus
Zone 3 – 8
AI generated
Arugula
Eruca sativa
Zone 5a – 10b
AI generated
Alfalfa
Medicago sativa
Zone 3a – 10a
AI generated
Hardiness ranges come from PlantoScan's plant database; gardeners in Illinois's colder or warmer edge zones should check each plant's full range.
When Is the Last Frost in Illinois?
Across most Illinois ZIP codes, the average last spring frost falls between April 7 and April 26, from April 4 in Godfrey to April 30 in Waukegan. Tender vegetables such as tomatoes go out 1 to 2 weeks after the local date.
The last and first frost dates for Illinois cities include the safer 90% planting date, the fall frost date, growing season length and a tomato planting table for each city.
Frequently Asked Questions
- What planting zone is Illinois?
- Illinois spans USDA hardiness zones 5a to 7a on the 2023 USDA Plant Hardiness Zone Map. Zone 6a is the most common, covering 42% of the state's 1,545 ZIP codes, and zones 5b to 7a together cover 98%.
- What hardiness zone is Chicago, Illinois?
- Chicago is in USDA hardiness zone 6a (ZIP 60608), where the average coldest winter night reaches −10 °F to −5 °F. Its average last spring frost is April 10 and its first fall frost November 5.
- What hardiness zone is Aurora, Illinois?
- Aurora is in USDA hardiness zone 5b (ZIP 60505), where the average coldest winter night reaches −15 °F to −10 °F. Its average last spring frost is April 19 and its first fall frost October 23.
- What hardiness zone is Naperville, Illinois?
- Naperville is in USDA hardiness zone 5b (ZIP 60540), where the average coldest winter night reaches −15 °F to −10 °F. Its average last spring frost is April 28 and its first fall frost October 16.
- What is the coldest hardiness zone in Illinois?
- Zone 5a (−20 °F to −15 °F) is the coldest zone in Illinois, found in 28 ZIP codes around Freeport and Galena. The warmest is zone 7a (0 °F to 5 °F), around Belleville and O'Fallon.
Zones: 2023 USDA Plant Hardiness Zone Map ZIP code table, USDA Agricultural Research Service and the PRISM Climate Group, Oregon State University, used without changes. Frost dates: NOAA National Centers for Environmental Information, 1991–2020 U.S. Climate Normals. City locations and populations: U.S. Census Bureau Gazetteer files and Vintage 2024 population estimates. PlantoScan is not affiliated with or endorsed by these agencies.