Williamson, Illinois, sits in USDA hardiness zone 6b — a zone band wide enough that plant choice, not possibility, is the interesting question.
These conditions suit cabbage, hazelnut, lavender, and collard greens — a starting list any specific site will trim or extend with its own soil, sun, and drainage.
Even in Williamson, 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 Williamson 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 Williamson — soil, climate, flood, and parcel records. How we handle your address.
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Williamson — the short answer
Williamson, Illinois: USDA zone 6b, about 222 days between hard freezes, across 749 acres of town.
- USDA zone
- 6b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 28
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Nov 5
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~222
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 749 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 6b is Williamson's average, not your lot's — a low corner or a tree line moves it. Against Williamson's 222-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Williamson
Each reading below is measured for Williamson itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredWilliamson runs about 222 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
MeasuredWilliamson sits in USDA hardiness zone 6b.
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 Williamson is in
Williamson sits in the Interior River Valleys and Hills — EPA Level III, inside the wider Eastern Temperate Forests. That is read at Williamson's own centroid rather than borrowed from Madison County.
What Grows in Williamson
Every plant below cleared Williamson's own zone 6b and its 222-day season. Each card opens that plant's Illinois profile. How we score.
Is it too late to plant in Williamson?
Almost never — the real question is what to plant next. 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 5 — 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 Williamson
Survey cells within 31 miles of Williamson checked for spotted lanternfly, none carrying a detection — a surveyed negative, not an absence of looking. Nearest documented record 207 miles off. What to watch for.
What's on the federal record near Williamson
Closest first, within ~10 miles of Williamson. Listing isn't leaking, and distance isn't exposure.
- C&C AUTOBODYBrownfields · 1100 ft
- B & B Towing & AutomotiveUnderground Storage Tanks · 1.0 mi
- Wray Bros MarketUnderground Storage Tanks · 1.1 mi
- AMOCO, MEYERBrownfields · 1.1 mi
- Livingston ShellUnderground Storage Tanks · 1.2 mi
- CELTIC AUTO SALES & SERVICEBrownfields · 1.6 mi
- Olive TownshipUnderground Storage Tanks · 1.7 mi
- SOUTHSIDES RTE 66 AUTOBODY INCBrownfields · 1.8 mi
- Staunton Fuel & MaterialsUnderground Storage Tanks · 2.2 mi
- CVS PHARMACY 10774Brownfields · 2.2 mi
- ED KD MOTORSBrownfields · 2.2 mi
- DOLLAR GENERAL STORE 2588Brownfields · 2.2 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Williamson'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 Williamson.
Total Sites
122
within ~10 miles of Williamson
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
within ~10 miles of Williamson
Severity Distribution
within ~10 miles of Williamson
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Williamson, two things run higher than the national average within ~10 miles of Williamson — PFAS (4 sites) and Underground Storage Tanks (83 sites). Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in Williamson
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 Williamson average
Your land is one point inside Williamson
Everything above resolves to Williamson as a whole — one PHZM band and one 28°F frost record, read across 749 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 Williamson Average
Williamson Average
- ●USDA Zones 6b, averaged across Williamson
- ●One soil character for all of Williamson
- ●Frost dates read at Williamson's scale: Mar 28 to Nov 5
YOUR Parcel
- ✓Your exact zone, not Williamson's 6b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Williamson
Pull a site-specific report for your exact address in Williamson, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Williamson averages can't show:
We read public map data around Williamson — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Williamson average
How we know this about Williamson
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 Williamson’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 Williamson
When does frost risk typically end in Williamson?
The last hard freeze (28°F) in Williamson 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.
When is the first frost in Williamson?
The first hard freeze (28°F) in Williamson typically arrives around Nov 5, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 22, so the watching starts about Oct 6 — about 222 days after the spring freeze cleared.
How long is the growing season in Williamson?
Measured between 28°F hard freezes, Williamson sees about 222 frost-free days — roughly Mar 28 through Nov 5, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 18 to Oct 22, about 187 days.
Is the soil safe to grow vegetables in Williamson?
The federal record around Williamson is a meaningful one — 122 documented sites, mostly Underground Storage Tanks entries (83), the nearest Brownfields 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 Williamson?
From about Oct 6 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 5 (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 5. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Williamson's scale — its 6b band and its 222-day season. Your yard writes its own version of Williamson'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 Williamson’s own scale
7 of the readings below were taken at Williamson's own scale — its own ~222-day season between 28°F freezes, the 749 acres it covers and 122 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Williamson's own USDA hardiness band, zones 6bUSDA PHZM 2023
- Williamson's own 28°F hard-freeze dates, about Mar 28 and Nov 5 and the ~222-day span between themNOAA 1991–2020 Climate Normals
- 122 documented contamination sites on the federal record near Williamson, the closest Brownfields record about 0.2 miles out from the town centreFederal environmental registers
- Williamson's boundary and the 749 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6b and a ~222-day seasonGrowable Ground crop-matching engine
- The ecoregion at Williamson's own centroid, the Interior River Valleys and HillsUS EPA Level III Ecoregions
- Lanternfly survey cells around Williamson checked, none carrying a detectionlydemapr (De Bona & Helmus), 10 km survey lattice
Inherited from a wider read
- Soil character — no town-scale survey exists, so Williamson's 749 acres read through its county's SSURGO summaryfrom Madison County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Madison 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 Madison County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Williamson's 749 acreswhy one lot differs from the next →
- Which side of Williamson you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 749 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Brownfields 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 Williamson-wide figureread your own land →
More in Illinois
Wider growing context
What grows across IllinoisWilliamson sits outside our named growing regions, so Illinois as a whole is its closest context here.
Nearby growing guides