Cook County, in Illinois, sits in USDA hardiness zone 6b — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
A short list that earns its place here — cabbage, hazelnut, lavender, and collard greens — with any one site's soil, sun, and drainage making the final cut.
Cook County lies within Chicagoland (Chicago metro / lakeshore) — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Cook County holds more than one microclimate.
Soils and elevations shift across Cook 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 Cook County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Cook County — the short answer
Cook County, Illinois: USDA zone 6b, about 234 days between hard freezes, across 605K acres.
- USDA zone
- 6b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 28
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Nov 17
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~234
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 605K 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 6b is Cook County's average, not your lot's — a low corner or a tree line moves it. Against Cook County's 234-day season, see what your own ground reads.
One county, several growing seasons
Cook County's hard-freeze record runs about 234 days between freezes — but that is the county-wide average, and several towns inside it carry a markedly different season in their own 30-year record: Barrington Hills at about 196 days (against the county's ~234).
Those are measured records, not estimates. If you garden in one of these pockets, plant against your own town's season rather than the county's ~234-day average.
NOAA Regional Climate Centers ACIS (1991–2020), 30-year daily minimum record. Only held-out towns carrying their own record are named — a town with no record of its own is absent rather than estimated, and a county with nothing qualifying shows no spread at all.
Heat in Cook County
Across a year, Cook County accumulates about 3,040 growing degree days above 50°F, about 343 fewer than the middle Illinois county — ahead of 24 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 Cook County
Across Cook County, the ground is predominantly Mollisols, where Ozaukee, Markham, and Ashkum are the most extensive named soil series. The soil is generally moderately well drained with a silt loam surface. Topsoil pH runs about 6.5–6.8, neutral. Rainfall drains through hydrologic group D soils.
Soil order
Mollisols
Drainage
Moderately well drained
Prime farmland
18%
Hydric soils
22%
Soil still varies lot by lot — soil types explained.
How the ground varies across Cook County
The USDA soil survey maps 33% of Cook County as moderately well drained — but another 33% drains differently: 12% poorly drained, 11% somewhat poorly drained.
Ozaukee is the most extensive named soil at 10% of mapped acres, then Markham (9%) and Ashkum (6%).
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 Cook County
Each reading below is measured for Cook 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 Cook County are moderately well drained, in hydrologic group D — roughly the middle of the drainage range.
This is close to the middle most vegetables prefer: it holds enough water to carry a crop between rains without staying waterlogged. The catch is that a wet spring or a low corner can still tip it soggy.
Plant on the site as-is for most crops, but keep the lowest, slowest-draining beds for moisture-tolerant plantings.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Cook County runs about pH 6.5–6.8, 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
Wet ground
MeasuredAbout 22% of Cook County is mapped as hydric — wetland — soil.
If your lot falls in one of those pockets, a standard in-ground bed will fight waterlogging all season, and roots that need air will struggle.
Check how your own ground drains before you dig; raised beds or moisture-loving plantings turn a wet corner from a problem into a niche.
USDA NRCS SSURGO
Season length
MeasuredCook County runs about 234 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
The kind of country Cook County is in
Cook 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 Cook County
We scored all 1,086 plants against Cook County's own USDA zone 6b and its own 234-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 Cook County?
Too late for some crops, right on time for others — a growing season is a sequence, not a deadline. Cool-season crops can go in from around Feb 28; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 28 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 17 — 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.
Documented around Cook County
Spotted lanternfly documented 0 miles from Cook County, first recorded 2023. What to watch for.
- Japanese beetle94 documented records
- monarch butterfly2,575 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Cook County
USGS estimates 6,964 lb of Glyphosate on Cook County farmland in 2019, its largest by weight, ahead of Metolachlor & Metolachlor-s (3,388 lb) and Metolachlor-s (2,822 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 Cook County — and how to grow with it.
We checked the federal record across Cook County — 15,546 documented sites across 7 of the 9 source types we track.
The most significant on record: 220 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Cook County carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds with clean imported soil grow well almost anywhere in the meantime.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Cook County
Closest first, across Cook County. Listing isn't leaking, and distance isn't exposure.
- 700 W. ErieUnderground Storage Tanks · 350 ft
- CHICAGO TRIBUNE COBrownfields · 400 ft
- WATERSAVER FAUCET COBrownfields · 400 ft
- WATERSAVER FAUCET COToxics Release Inventory · 400 ft
- AMERITECHBrownfields · 550 ft
- Il Bell Telephone CoUnderground Storage Tanks · 550 ft
- Chicago Tribune CoUnderground Storage Tanks · 800 ft
- BT Office ProductsUnderground Storage Tanks · 800 ft
- Salvation ArmyUnderground Storage Tanks · 850 ft
- Special Ser Co IncUnderground Storage Tanks · 950 ft
- CHICAGO AVE BRIDGEBrownfields · 950 ft
- CHICAGO DOTBrownfields · 1000 ft
6 more sites are on the record inside the same radius. See them on the map
Measured from Cook 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 Cook County.
Severity Distribution
across Cook County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Cook County, two things run higher than the national average across Cook County — Toxics Release Inventory (1,336 sites) and Superfund (220 sites). That's not a problem with your land — it's information about it.
Toxics Release Inventory: TRI facilities report annual chemical releases to air, water, and land.
Superfund: Superfund sites represent the most severe contamination in the federal system.
Check prevailing wind direction — downwind parcels face higher exposure than upwind or crosswind locations.
Commission professional soil testing before any food production (test for heavy metals, VOCs, and SVOCs).
Check your specific parcel in Cook 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 Cook County average
Your land is one point inside Cook County
Everything above resolves to Cook County as a whole — one PHZM band and one county frost record, read across 605K 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 Cook County Average
Cook County Average
- ●USDA Zones 6b, averaged across Cook County
- ●One soil character for all of Cook County
- ●Frost dates read at Cook County's scale: Mar 28 to Nov 17
YOUR Parcel
- ✓Your exact zone, not Cook County's 6b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Cook County
Pull a site-specific report for your exact address in Cook County, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Cook County averages can't show:
We read public map data around Cook County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Cook County average
How we know this about Cook 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 Cook County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Cook County
When does frost risk typically end in Cook County?
The last hard freeze (28°F) in Cook County typically lands around Mar 28, 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 18.
How long is the growing season in Cook County?
Measured between 28°F hard freezes, Cook County sees about 234 frost-free days — roughly Mar 28 through Nov 17, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 18 to Nov 3, about 199 days.
Is the soil safe to grow vegetables in Cook County?
The federal record around Cook County runs heavier than most — 15,546 documented sites, mostly Underground Storage Tanks entries (7,555), the nearest Underground Storage Tanks record under a tenth of a mile out — so test the soil before planting food in the ground, and raised beds with clean imported soil grow well in the meantime. Even here, proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what's recorded and where.
Everything above is measured at Cook County's scale — its 6b band and its 234-day season. Your yard writes its own version of Cook 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 Cook County’s own scale
9 of the readings below were taken at Cook County's own scale — its own ~234-day span between 28°F freezes, the 3 most extensive soil series mapped here and 15,546 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Cook County's own USDA hardiness band, zones 6bUSDA PHZM 2023
- Cook County's own 28°F hard-freeze dates and its ~234-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Cook CountyUSDA NRCS SSURGO
- 15,546 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record under a tenth of a mile outFederal environmental registers
- Cook County's boundary and the 604,755 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6b and a ~234-day seasonGrowable Ground crop-matching engine
- Cook County sitting wholly inside the Central Corn Belt PlainsUS EPA Level III Ecoregions
- Open occurrence records documented in Cook County for 2 tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Cook 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 Cook County — the ~234 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 Cook County's 604,755 acreswhy one lot differs from the next →
- Which of those 15,546 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 Cook Countyread your own land →