Mercer County, in Illinois, sits in USDA hardiness zone 5b — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Expect cabbage, cranberry, lavender, and collard greens to be strong candidates here; the deciding factors on any one parcel stay local — soil, sun, and drainage.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Mercer County holds more than one microclimate.
Soils and elevations shift across Mercer 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 Mercer County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Mercer County — the short answer
Mercer County, Illinois: USDA zone 5b, about 203 days between hard freezes, across 359K acres.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 7
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 27
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~203
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 359K 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 Mercer County's average, not your lot's — a low corner or a tree line moves it. Against Mercer County's 203-day season, see what your own ground reads.
Heat in Mercer County
Across a year, Mercer County accumulates about 3,031 growing degree days above 50°F, about 352 fewer than the middle Illinois county — ahead of 21 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 Mercer County
Across Mercer County, the ground is predominantly Alfisols, where Muscatune, Hickory, and Osco are the most extensive named soil series. The soil is generally well drained with a silt loam surface. Topsoil pH runs about 6.2–6.7, slightly acidic. Rainfall drains through hydrologic group B soils.
Soil order
Alfisols
Drainage
Well drained
Prime farmland
37%
Hydric soils
12%
Soil still varies lot by lot — soil types explained.
How the ground varies across Mercer County
The USDA soil survey maps 54% of Mercer County as well drained — but another 45% drains differently: 27% somewhat poorly drained, 11% poorly drained.
Muscatune is the most extensive named soil at 12% of mapped acres, then Hickory (11%) and Osco (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 Mercer County
Each reading below is measured for Mercer 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 Mercer 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 Mercer County runs about pH 6.2–6.7, 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
MeasuredMercer County runs about 203 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
MeasuredMercer 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 Mercer County is in
Mercer 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 Mercer County
We scored all 1,086 plants against Mercer County's own USDA zone 5b and its own 203-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 Mercer County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Mar 10; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 7 (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. With a season this long, “too late” mostly means “switch crops” — second sowings and a full fall garden are the norm, with garlic closing the year.
Documented around Mercer County
- Japanese beetle2 documented records
- monarch butterfly24 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Mercer County
USGS estimates 265,688 lb of Glyphosate on Mercer County farmland in 2019, its largest by weight, ahead of Metolachlor & Metolachlor-s (97,626 lb) and Atrazine (93,377 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 Mercer County — and how to grow with it.
We checked the federal record across Mercer County — 153 documented sites across 6 of the 9 source types we track.
The most significant on record: 5 Toxics Release Inventory facilities. Active industrial facilities reporting chemical releases to air, water, and land.
The federal record across Mercer 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 Mercer County
Closest first, across Mercer County. Listing isn't leaking, and distance isn't exposure.
- Blick & Blick Oil, Inc.Underground Storage Tanks · 2100 ft
- WARECO SERV STA #560Brownfields · 2100 ft
- Deep Rock StationUnderground Storage Tanks · 2100 ft
- Midway Oil CoUnderground Storage Tanks · 2300 ft
- Virgil Anderson Oil CoUnderground Storage Tanks · 2300 ft
- Farmers Grain & Coal CoUnderground Storage Tanks · 2300 ft
- Aledo AmocoUnderground Storage Tanks · 2300 ft
- Loyd LafeverUnderground Storage Tanks · 2400 ft
- HENDERSON FORD SALES INCBrownfields · 2600 ft
- City of AledoUnderground Storage Tanks · 2600 ft
- Fell & Fell Standard SerUnderground Storage Tanks · 2600 ft
- Henderson Ford Sales IncUnderground Storage Tanks · 0.5 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Mercer 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 Mercer County.
Total Sites
153
across Mercer County
Risk Level
Moderate
Highest-severity
5 Toxics Release Inventory facilities
Sources Checked
across Mercer County
Severity Distribution
across Mercer County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Mercer County, CAFO runs higher than the national average — 22 sites across Mercer County. Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
CAFO: CAFOs pose a different contamination profile than chemical sources.
Wash all produce consumed raw thoroughly, especially leafy greens grown near CAFOs.
Check your specific parcel in Mercer 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 Mercer County average
Your land is one point inside Mercer County
Everything above resolves to Mercer County as a whole — one PHZM band and one county frost record, read across 359K 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 Mercer County Average
Mercer County Average
- ●USDA Zones 5b, averaged across Mercer County
- ●One soil character for all of Mercer County
- ●Frost dates read at Mercer County's scale: Apr 7 to Oct 27
YOUR Parcel
- ✓Your exact zone, not Mercer County's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Mercer County
Pull a site-specific report for your exact address in Mercer County, Illinois — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Mercer County averages can't show:
We read public map data around Mercer County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Mercer County average
How we know this about Mercer 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 Mercer County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Mercer County
When does frost risk typically end in Mercer County?
The last hard freeze (28°F) in Mercer County typically lands around Apr 7, 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 28.
How long is the growing season in Mercer County?
Measured between 28°F hard freezes, Mercer County sees about 203 frost-free days — roughly Apr 7 through Oct 27, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 28 to Oct 13, about 168 days.
Is the soil safe to grow vegetables in Mercer County?
The federal record around Mercer County shows 153 documented sites, mostly Underground Storage Tanks entries (91), the nearest Underground Storage Tanks record about 0.4 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 Mercer County's scale — its 5b band and its 203-day season. Your yard writes its own version of Mercer 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 Mercer County’s own scale
9 of the readings below were taken at Mercer County's own scale — its own ~203-day span between 28°F freezes, the 3 most extensive soil series mapped here and 153 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Mercer County's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Mercer County's own 28°F hard-freeze dates and its ~203-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Mercer CountyUSDA NRCS SSURGO
- 153 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 0.4 miles outFederal environmental registers
- Mercer County's boundary and the 359,193 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~203-day seasonGrowable Ground crop-matching engine
- Mercer County sitting wholly inside the Interior River Valleys and HillsUS EPA Level III Ecoregions
- Open occurrence records documented in Mercer County for 2 tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Mercer 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 Mercer County — the ~203 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 Mercer County's 359,193 acreswhy one lot differs from the next →
- Which of those 153 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 Mercer Countyread your own land →