Iroquois County, in Illinois, sits in USDA hardiness zone 5b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
These conditions suit cabbage, cranberry, lavender, and collard greens — a starting list any specific site will trim or extend with its own soil, sun, and drainage.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Iroquois County holds more than one microclimate.
Soils and elevations shift across Iroquois County, so your frost dates and drainage aren't the county average. 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 Iroquois County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Iroquois County — the short answer
Iroquois County, Illinois: USDA zone 5b, about 197 days between hard freezes, across 715K acres.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 11
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 25
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~197
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 715K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 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 5b is Iroquois County's average, not your lot's — a low corner or a tree line moves it. Against Iroquois County's 197-day season, see what your own ground reads.
Heat in Iroquois County
Across a year, Iroquois County accumulates about 3,008 growing degree days above 50°F, about 375 fewer than the middle Illinois county — ahead of 19 of Illinois’s 102 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Iroquois County
Across Iroquois County, the ground is predominantly Mollisols, where Milford, Bryce, and Selma are the most extensive named soil series. The soil is generally poorly drained with a silty clay loam surface. Topsoil pH runs about 6.2–6.8, slightly acidic. Rainfall drains through hydrologic group C/D soils.
Soil order
Mollisols
Drainage
Poorly drained
Prime farmland
31%
Hydric soils
59%
Soil still varies lot by lot — soil types explained.
How the ground varies across Iroquois County
The USDA soil survey maps 56% of Iroquois County as poorly drained — but another 43% drains differently: 32% somewhat poorly drained, 3% excessively drained.
Milford is the most extensive named soil at 16% of mapped acres, then Bryce (14%) and Selma (9%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in Iroquois County
Each reading below is measured for Iroquois County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across Iroquois County are poorly drained, in hydrologic group C/D — ground that sheds water slowly.
Beds can stay saturated for days after heavy rain, and the roots of most vegetables, berries, and fruit trees suffocate or rot in soil that never drains.
Raised beds or mounded rows lift roots above the wet zone; choose water-tolerant crops for the lowest spots.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Iroquois County runs about pH 6.2–6.8, close to neutral.
This is the range most vegetables prefer — one correction you probably do not have to make, which is genuinely good news for a new bed.
Keep it there with compost rather than lime or sulfur, and only amend if your own soil test says otherwise.
USDA NRCS SSURGO
Season length
MeasuredIroquois County runs about 197 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredIroquois County sits in USDA hardiness zone 5b.
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 Iroquois County is in
Iroquois County sits in the Central Corn Belt Plains — EPA Level III, inside the wider Eastern Temperate Forests. One consistent ecological setting across the whole county.
What Grows in Iroquois County
We scored all 1,086 plants against Iroquois County's own USDA zone 5b and its own 197-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's Illinois profile.
Is it too late to plant in Iroquois County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Mar 14; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 11 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 25 — long-season crops need about 90 days of runway, quick greens only 30. The tail of the season still works: sixty-day crops into late summer, quick greens after, garlic last of all.
Documented around Iroquois County
- Japanese beetle3 documented records
- monarch butterfly28 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Iroquois County
USGS estimates 515,191 lb of Glyphosate on Iroquois County farmland in 2019, its largest by weight, ahead of Acetochlor (238,418 lb) and Atrazine (204,541 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across Iroquois County — and how to grow with it.
We checked the federal record across Iroquois County — 257 documented sites across 6 of the 9 source types we track.
The most significant on record: 6 Toxics Release Inventory facilities. Active industrial facilities reporting chemical releases to air, water, and land.
There's a meaningful federal record across Iroquois County — worth a look before you plant food, not a reason to hold back from growing. Proximity to a documented site is information, not a diagnosis of any one yard. A soil test before new food beds is the sensible precaution here, and the map shows exactly which sites sit where, so you can see what's actually near you.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Iroquois County
Closest first, across Iroquois County. Listing isn't leaking, and distance isn't exposure.
- Hn&WUnderground Storage Tanks · 1.5 mi
- Zum Mallen Concrete IncUnderground Storage Tanks · 1.7 mi
- UNITED MARINE CORPToxics Release Inventory · 1.8 mi
- Township Road DistUnderground Storage Tanks · 2.0 mi
- Casey's General StoreUnderground Storage Tanks · 2.1 mi
- Peterson ShellUnderground Storage Tanks · 2.1 mi
- Gocken AmocoUnderground Storage Tanks · 2.1 mi
- Former Peterson ShellUnderground Storage Tanks · 2.1 mi
- K AND J AUTO BODYBrownfields · 3.9 mi
- Carley Farms, Inc.Underground Storage Tanks · 4.3 mi
- Burns Implement Co., Inc.Underground Storage Tanks · 4.5 mi
- Onarga Radio TowerUnderground Storage Tanks · 4.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Iroquois County'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 Iroquois County.
Total Sites
257
across Iroquois County
Risk Level
Elevated
Highest-severity
6 Toxics Release Inventory facilities
Sources Checked
across Iroquois County
Severity Distribution
across Iroquois County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Iroquois County, two things run higher than the national average across Iroquois County — CAFO (5 sites) and PFAS (3 sites). That's not a problem with your land — it's information about it.
CAFO: CAFOs pose a different contamination profile than chemical sources.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Wash all produce consumed raw thoroughly, especially leafy greens grown near CAFOs.
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Check your specific parcel in Iroquois County
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 Iroquois County average
Your land is one point inside Iroquois County
Everything above resolves to Iroquois County as a whole — one PHZM band and one county frost record, read across 715K 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 county 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 county average.
Your Lot vs the Iroquois County Average
Iroquois County Average
- ●USDA Zones 5b, averaged across Iroquois County
- ●One soil character for all of Iroquois County
- ●Frost dates read at Iroquois County's scale: Apr 11 to Oct 25
YOUR Parcel
- ✓Your exact zone, not Iroquois County's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Iroquois County
Pull a site-specific report for your exact address in Iroquois County, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Iroquois County averages can't show:
We read public map data around Iroquois County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Iroquois County average
How we know this about Iroquois County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where Iroquois County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Iroquois County
When does frost risk typically end in Iroquois County?
The last hard freeze (28°F) in Iroquois County typically lands around Apr 11, 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 May 2.
How long is the growing season in Iroquois County?
Measured between 28°F hard freezes, Iroquois County sees about 197 frost-free days — roughly Apr 11 through Oct 25, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 2 to Oct 11, about 162 days.
Is the soil safe to grow vegetables in Iroquois County?
The federal record around Iroquois County is a meaningful one — 257 documented sites, mostly Underground Storage Tanks entries (196), the nearest Underground Storage Tanks record about 1.5 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.
Everything above is measured at Iroquois County's scale — its 5b band and its 197-day season. Your yard writes its own version of Iroquois County's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads Illinois's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Iroquois County’s own scale
9 of the readings below were taken at Iroquois County's own scale — its own ~197-day span between 28°F freezes, the 3 most extensive soil series mapped here and 257 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Iroquois County's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Iroquois County's own 28°F hard-freeze dates and its ~197-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Iroquois CountyUSDA NRCS SSURGO
- 257 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 1.5 miles outFederal environmental registers
- Iroquois County's boundary and the 715,140 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~197-day seasonGrowable Ground crop-matching engine
- Iroquois County sitting wholly inside the Central Corn Belt PlainsUS EPA Level III Ecoregions
- Open occurrence records documented in Iroquois County for 2 tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Iroquois County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Illinois grower plans around — written at state scale, so they stay on the state guidefrom Illinois
What this page can’t tell you
- How the season shifts across Iroquois County — the ~197 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Iroquois County's 715,140 acreswhy one lot differs from the next →
- Which of those 257 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over Iroquois Countyread your own land →