Warren County, in Illinois, sits in USDA hardiness zone 5b — a zone band wide enough that plant choice, not possibility, is the interesting question.
On paper, cabbage, cranberry, lavender, and collard greens all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Warren County holds more than one microclimate.
Soils and elevations shift across Warren 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 Warren County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Warren County — the short answer
Warren County, Illinois: USDA zone 5b, about 202 days between hard freezes, across 347K acres.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 8
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 27
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~202
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 347K 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 Warren County's average, not your lot's — a low corner or a tree line moves it. Against Warren County's 202-day season, see what your own ground reads.
Heat in Warren County
Across a year, Warren County accumulates about 3,084 growing degree days above 50°F, about 299 fewer than the middle Illinois county — ahead of 28 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 Warren County
Across Warren County, the ground is predominantly Mollisols, where Muscatune, Osco, and Sable are the most extensive named soil series. The soil is generally well drained with a silt loam surface. Topsoil pH runs about 6.0–6.6, slightly acidic. Rainfall drains through hydrologic group B soils.
Soil order
Mollisols
Drainage
Well drained
Prime farmland
52%
Hydric soils
13%
Soil still varies lot by lot — soil types explained.
How the ground varies across Warren County
The USDA soil survey maps 49% of Warren County as well drained — but another 51% drains differently: 31% somewhat poorly drained, 14% poorly drained.
Muscatune is the most extensive named soil at 20% of mapped acres, then Osco (17%) and Sable (11%).
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 Warren County
Each reading below is measured for Warren 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 Warren County are well drained, in hydrologic group B — ground that drains quickly.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Warren County runs about pH 6.0–6.6, 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
MeasuredWarren County runs about 202 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
MeasuredWarren 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 Warren County is in
Warren County sits in the Interior River Valleys and Hills — EPA Level III, inside the wider Eastern Temperate Forests. One consistent ecological setting across the whole county.
What Grows in Warren County
We scored all 1,086 plants against Warren County's own USDA zone 5b and its own 202-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 Warren County?
For most of the year, no — what changes is which crops still fit the days remaining. Cool-season crops can go in from around Mar 11; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 8 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 27 — long-season crops need about 90 days of runway, quick greens only 30. A long window like this one runs successions deep into fall — and even its last weeks take quick greens and garlic.
Documented around Warren County
- Japanese beetle1 documented records
- monarch butterfly44 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Warren County
USGS estimates 262,905 lb of Glyphosate on Warren County farmland in 2019, its largest by weight, ahead of Atrazine (116,357 lb) and Acetochlor (103,310 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 Warren County — and how to grow with it.
We checked the federal record across Warren County — 163 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.
The federal record across Warren County is a modest one — a typical footprint for a growing area. Nothing here calls for alarm; it's worth knowing which recorded sites sit closest to where you grow, and each one on the map carries its type and location. If one turns out to be a near neighbor, a one-time soil test settles the question.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Warren County
Closest first, across Warren County. Listing isn't leaking, and distance isn't exposure.
- Ormonde Depot & Yard AreaUnderground Storage Tanks · 2600 ft
- MONSANTO AG PRODUCTS COBrownfields · 1.7 mi
- IDOTBrownfields · 3.3 mi
- Monmouth State Garage #26Underground Storage Tanks · 3.3 mi
- MCCLURE FARMS, LLC - KIRKWOODCAFO · 3.3 mi
- FOOTE BRUCE CHEVROLET OLDS CAD INCBrownfields · 3.4 mi
- BP PIPELINES (NA) INC ORMONDEBrownfields · 3.4 mi
- Russ Motors BldgUnderground Storage Tanks · 3.4 mi
- Homegrown Properties-MonmouthUnderground Storage Tanks · 3.5 mi
- MARTIN AND CLARK COBrownfields · 3.5 mi
- Martin & Clark CoUnderground Storage Tanks · 3.5 mi
- Keister's Inc.Underground Storage Tanks · 3.5 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Warren 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 Warren County.
Total Sites
163
across Warren County
Risk Level
Moderate
Highest-severity
6 Toxics Release Inventory facilities
Sources Checked
across Warren County
Severity Distribution
across Warren County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Warren County, two things run higher than the national average across Warren County — CAFO (14 sites) and Underground Storage Tanks (102 sites). That's not a problem with your land — it's information about it.
CAFO: CAFOs pose a different contamination profile than chemical sources.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Wash all produce consumed raw thoroughly, especially leafy greens grown near CAFOs.
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in Warren 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 Warren County average
Your land is one point inside Warren County
Everything above resolves to Warren County as a whole — one PHZM band and one county frost record, read across 347K 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 Warren County Average
Warren County Average
- ●USDA Zones 5b, averaged across Warren County
- ●One soil character for all of Warren County
- ●Frost dates read at Warren County's scale: Apr 8 to Oct 27
YOUR Parcel
- ✓Your exact zone, not Warren County's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Warren County
Pull a site-specific report for your exact address in Warren County, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Warren County averages can't show:
We read public map data around Warren County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Warren County average
How we know this about Warren 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 Warren County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Warren County
When does frost risk typically end in Warren County?
The last hard freeze (28°F) in Warren County typically lands around Apr 8, 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 29.
How long is the growing season in Warren County?
Measured between 28°F hard freezes, Warren County sees about 202 frost-free days — roughly Apr 8 through Oct 27, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 29 to Oct 13, about 167 days.
Is the soil safe to grow vegetables in Warren County?
The federal record around Warren County shows 163 documented sites, mostly Underground Storage Tanks entries (102), the nearest Underground Storage Tanks record about 0.5 miles out — a typical footprint for a growing area, and proximity to a documented site is information, not a diagnosis of any one yard. It's worth seeing which recorded sites sit closest to where you grow, and testing the soil before new food beds near any of them.
Everything above is measured at Warren County's scale — its 5b band and its 202-day season. Your yard writes its own version of Warren 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 Warren County’s own scale
9 of the readings below were taken at Warren County's own scale — its own ~202-day span between 28°F freezes, the 3 most extensive soil series mapped here and 163 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Warren County's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Warren County's own 28°F hard-freeze dates and its ~202-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Warren CountyUSDA NRCS SSURGO
- 163 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 0.5 miles outFederal environmental registers
- Warren County's boundary and the 347,110 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~202-day seasonGrowable Ground crop-matching engine
- Warren County sitting wholly inside the Interior River Valleys and HillsUS EPA Level III Ecoregions
- Open occurrence records documented in Warren County for 2 tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Warren 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 Warren County — the ~202 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 Warren County's 347,110 acreswhy one lot differs from the next →
- Which of those 163 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 Warren Countyread your own land →