Illiopolis, Illinois, sits in USDA hardiness zone 6a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Well-matched crops include cabbage, hazelnut, lavender, and collard greens, and the gap between "grows in the area" and "grows in your yard" is closed by soil, sun, and drainage.
Even in Illiopolis, no two yards are alike.
A low spot, a south-facing slope, or a stand of trees moves the frost date and sun across a single Illiopolis lot. Enter your address and we'll score 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around Illiopolis — soil, climate, flood, and parcel records. How we handle your address.
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Illiopolis — the short answer
Illiopolis, Illinois: USDA zone 6a, about 213 days between hard freezes, across 433 acres of town.
- USDA zone
- 6a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 2
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Nov 1
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~213
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 433 acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are this town’s own 28°F normals: light frosts run a few weeks past them, and tender transplants usually wait 2–3 weeks after the last hard freeze.
Hardiness Zone Range
Zone 6a is Illiopolis's average, not your lot's — a low corner or a tree line moves it. Against Illiopolis's 213-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Illiopolis
Each reading below is measured for Illiopolis itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredIlliopolis runs about 213 days between hard freezes — a long growing season.
There is slack for succession plantings and slow-finishing crops: many vegetables can be sown twice, and the heat-lovers have time to ripen fully.
Plan a second sowing of quick crops after the first comes out, and use the fall window most gardeners let sit idle.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredIlliopolis sits in USDA hardiness zone 6a.
The zone sets which perennials, shrubs, and fruit trees live through an average winter here — a plant rated for a colder zone is a safe bet, one rated warmer needs winter protection or gets treated as an annual.
Match perennials and fruit to the zone before you buy, so nothing you plant is a gamble against the cold.
USDA PHZM 2023
The kind of country Illiopolis is in
Illiopolis sits in the Central Corn Belt Plains — EPA Level III, inside the wider Eastern Temperate Forests. That is read at Illiopolis's own centroid rather than borrowed from Sangamon County.
What Grows in Illiopolis
Every plant below cleared Illiopolis's own zone 6a and its 213-day season. Each card opens that plant's Illinois profile. How we score.
Is it too late to plant in Illiopolis?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Mar 5; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 2 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 1 — long-season crops need about 90 days of runway, quick greens only 30. Here the season winds down slowly: late sowings, a real autumn harvest, and garlic in the ground before the first hard freeze.
What's on the federal record near Illiopolis
Closest first, within ~10 miles of Illiopolis. Listing isn't leaking, and distance isn't exposure.
- ROHM & HAASToxics Release Inventory · 1100 ft
- Curry Ice & Coal of Illiopolis, Inc.Underground Storage Tanks · 1100 ft
- Fast StopUnderground Storage Tanks · 1200 ft
- Monical Oil / Former Stewarts ServiceUnderground Storage Tanks · 2000 ft
- Illiopolis Cud #12Underground Storage Tanks · 2000 ft
- Illiopolis Grain CoUnderground Storage Tanks · 2100 ft
- Illiopolis Auto Repair SerUnderground Storage Tanks · 0.5 mi
- Farm Supply Ser IncUnderground Storage Tanks · 0.5 mi
- Graves Motor CoUnderground Storage Tanks · 0.5 mi
- Illiopolis Village OfUnderground Storage Tanks · 0.7 mi
- Former Deanna Hamm PropertyUnderground Storage Tanks · 0.9 mi
- FORMOSA PLASTICS CORPToxics Release Inventory · 1.4 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Illiopolis's center, not your beds. Run your own address for what's upwind of you specifically.
Environmental Intelligence
The counts behind that headline — every source type on the record near Illiopolis.
Total Sites
58
within ~10 miles of Illiopolis
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
within ~10 miles of Illiopolis
Severity Distribution
within ~10 miles of Illiopolis
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Illiopolis, Underground Storage Tanks runs higher than the national average — 37 sites within ~10 miles of Illiopolis. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in Illiopolis
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,086 plant recommendations.
25+ data sources read at your address, not the Illiopolis average
Your land is one point inside Illiopolis
Everything above resolves to Illiopolis as a whole — one PHZM band and one 28°F frost record, read across 433 acres. Your parcel is one point inside that footprint. Slope, tree cover, a low spot that pools cold air, and what is in the soil are all resolved at the address, and none of them are visible at town scale. That is the honest boundary of this page, and the reason the next step is a reading of your own ground rather than a better local average.
Your Lot vs the Illiopolis Average
Illiopolis Average
- ●USDA Zones 6a, averaged across Illiopolis
- ●One soil character for all of Illiopolis
- ●Frost dates read at Illiopolis's scale: Apr 2 to Nov 1
YOUR Parcel
- ✓Your exact zone, not Illiopolis's 6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Illiopolis
Pull a site-specific report for your exact address in Illiopolis, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Illiopolis averages can't show:
We read public map data around Illiopolis — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Illiopolis average
How we know this about Illiopolis
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this town’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Illiopolis’s own record; boundaries and acreage from US Census TIGER/Line 2025; the contamination records from the federal sources named in their beats above. Soil is not read at town grain anywhere on this page — there is no town-resolution survey in our data, which is why you will find no soil grid here rather than a statewide one wearing a local label. The resolution ledger below names every figure this page inherited.
Common questions about Illiopolis
When does frost risk typically end in Illiopolis?
The last hard freeze (28°F) in Illiopolis typically lands around Apr 2, per NOAA 1991–2020 climate normals — earlier than the light-frost dates most charts quote. That marks the hard freeze, not the last light frost — lighter frosts keep biting past it, which is why tender transplants here wait until about Apr 23.
When is the first frost in Illiopolis?
The first hard freeze (28°F) in Illiopolis typically arrives around Nov 1, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 18, so the watching starts about Oct 2 — about 213 days after the spring freeze cleared.
How long is the growing season in Illiopolis?
Measured between 28°F hard freezes, Illiopolis sees about 213 frost-free days — roughly Apr 2 through Nov 1, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 23 to Oct 18, about 178 days.
Is the soil safe to grow vegetables in Illiopolis?
The federal record around Illiopolis is a meaningful one — 58 documented sites, mostly Underground Storage Tanks entries (37), the nearest Toxics Release Inventory record about 0.2 miles out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
How do I protect my plants from frost in Illiopolis?
From about Oct 2 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Nov 1 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Nov 1. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Illiopolis's scale — its 6a band and its 213-day season. Your yard writes its own version of Illiopolis's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
What this page reads at Illiopolis’s own scale
6 of the readings below were taken at Illiopolis's own scale — its own ~213-day season between 28°F freezes, the 433 acres it covers and 58 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Illiopolis's own USDA hardiness band, zones 6aUSDA PHZM 2023
- Illiopolis's own 28°F hard-freeze dates, about Apr 2 and Nov 1 and the ~213-day span between themNOAA 1991–2020 Climate Normals
- 58 documented contamination sites on the federal record near Illiopolis, the closest Toxics Release Inventory record about 0.2 miles out from the town centreFederal environmental registers
- Illiopolis's boundary and the 433 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6a and a ~213-day seasonGrowable Ground crop-matching engine
- The ecoregion at Illiopolis's own centroid, the Central Corn Belt PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Illiopolis's 433 acres read through its county's SSURGO summaryfrom Sangamon County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Sangamon County
- The growing challenges every Illinois grower plans around — written at state scale, so they stay on the state guidefrom Illinois
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Sangamon County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Illiopolis's 433 acreswhy one lot differs from the next →
- Which side of Illiopolis you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 433 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Toxics Release Inventory record about 0.2 miles out, measured from the town centrehow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — measured at your address, and averaged away by any Illiopolis-wide figureread your own land →
More in Illinois
Wider growing context
What grows across IllinoisIlliopolis sits outside our named growing regions, so Illinois as a whole is its closest context here.
Nearby growing guides