What USDA hardiness zone is Carroll County, Illinois?

Carroll County, Illinois spans USDA hardiness zones 5a to 5b. 86% of its ZIP codes are zone 5a, so there is no single zone for the county.

When is the last spring frost in Carroll County, Illinois?

The median last spring freeze runs April 13 – May 2 across the 4 NOAA weather stations serving Carroll County, Illinois, from NOAA 1991-2020 Climate Normals. Half of years freeze later than the median.

Illinois

Planting zones in Carroll County, Illinois

This county spans USDA zones 5a to 5b, so there is no single zone for Carroll County and anyone who gives you one is rounding. 86% of its ZIP codes are zone 5a; the rest are not.

USDA zones 5a–5b 2 zones across 7 ZIP codes

ZIP codes 7 7 have a NOAA station within range

Weather stations 4 NOAA 1991–2020 normals, across 445 sq mi

Your ZIP code

Get the exact answer for your address

Everything above describes Carroll County, Illinois as a whole. Hardiness zones and freeze dates are published per ZIP code, so yours is exact — enter it and this page will tell you your zone, which NOAA station it comes from and how far away that station is.

The growing season in Carroll County is closing

Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives October 7 – October 26 across the 4 NOAA stations serving this county .

Your next season already has a date

The first job of it is 🧅 Green Onions, start indoors, around February 16 – March 7 — counted back from a last spring freeze of April 13 – May 2 here.

Every spring date for your ZIP →

These are ranges across the whole county. The ZIP lookup above gives the dates from your own nearest station instead.

All 4 stations agreeAt least one station

Every one of the 4 NOAA stations serving this county counts May 2 – October 7 as growing season (158 days). Widening to any single station gives April 13 – October 26 (196 days).

That is a 38-day difference inside one county — which is why this page gives ranges rather than a single planting date. The ZIP lookup above resolves it to one station.

Which zone you are in depends where you are

Carroll County covers 2 hardiness zones. A guide that gives the county one zone has picked whichever is largest and rounded everyone else into it — fine for the 86% in zone 5a and wrong for the other 14%. Here is the actual split.

Zone	ZIP codes	Share
5a	6	86%
5b	1	14%

Zones are published per ZIP code, so yours is exact even though the county's is not. The hardiness tool will tell you which one you are in.

Your freeze dates

Last spring freeze April 13 – May 2

First fall freeze October 7 – October 26

Across the 4 NOAA stations serving this county. These are medians — half of years freeze later than the date shown — so treat the later end of each range as the cautious one.

The growing season runs 154–195 days depending which station you are nearest, as published by NOAA rather than computed from the dates above. Summer highs average 80.8–83.3 °F in June–August. Summer rain over the same months runs 11.3–14.3" across those 4 stations, against the rough inch a week — about 13 inches over the same 92 days — that a vegetable garden is usually reckoned to want. At the middle station that is covered, so watering in Carroll County is for the gaps between storms rather than the whole season. The inches are NOAA's published normals; the inch a week is a rule of thumb, and it takes no account of a 83 °F summer afternoon drying the soil faster than a cool one.

Every ZIP code in Carroll County

Zones are published per ZIP code, not per county, so this is the exact answer rather than the county's average. The station column is the nearest one to that ZIP code's centroid and how far away it is — the same figure the tools use, shown here so you can see which ZIP codes are well covered and which are reaching.

ZIP code	USDA zone	Nearest NOAA station	Distance
61014	5a	Mt Carroll, IL	15.9 km
61046	5a	Mt Carroll, IL	14.2 km
61051	5a	Polo 5Nw, IL	14.0 km
61053	5a	Mt Carroll, IL	2.5 km
61074	5a	Mt Carroll, IL	11.8 km
61078	5a	Freeport Waste Wtp, IL	17.8 km
61285	5b	Fulton L&D #13, IL	12.2 km

ZIP-code positions are area centroids, so a large rural ZIP code's listed distance is measured from the middle of its area rather than from any particular address in it.

When to start seeds in Carroll County

Every date below is anchored on the last spring freeze at each station and reported as a range across all 4 of them, because no one station speaks for the county.

Crop	Job	When	Offset
🧅 Green Onions	Start indoors	February 16 – March 7	8 wk before
🌶️ Peppers	Start indoors	February 16 – March 7	8 wk before
🥦 Broccoli	Start indoors	March 2 – March 21	6 wk before
🥬 Cabbage	Start indoors	March 2 – March 21	6 wk before
🥬 Collards	Start indoors	March 2 – March 21	6 wk before
🥬 Kale	Start indoors	March 2 – March 21	6 wk before
🥬 Leaf Lettuce	Start indoors	March 2 – March 21	6 wk before
🫛 Peas	Direct sow	March 2 – March 21	6 wk before
🥬 Spinach	Direct sow	March 2 – March 21	6 wk before
🍠 Sweet Potato	Start indoors	March 2 – March 21	6 wk before
🍅 Tomatoes	Start indoors	March 2 – March 21	6 wk before
🥬 Bok Choy	Start indoors	March 9 – March 28	5 wk before
🥬 Kohlrabi	Start indoors	March 9 – March 28	5 wk before
🥬 Swiss Chard	Start indoors	March 9 – March 28	5 wk before
🥬 Arugula	Direct sow	March 16 – April 4	4 wk before
🥬 Baby Salad Greens	Direct sow	March 16 – April 4	4 wk before
🥕 Beets	Direct sow	March 16 – April 4	4 wk before
🧅 Green Onions	Direct sow	March 16 – April 4	4 wk before
🥬 Mustard Greens	Direct sow	March 16 – April 4	4 wk before
🌶️ Okra	Start indoors	March 16 – April 4	4 wk before
🌱 Radishes	Direct sow	March 16 – April 4	4 wk before
🥔 Turnips	Direct sow	March 16 – April 4	4 wk before
🥬 Cabbage	Set out	March 23 – April 11	3 wk before
🥕 Carrots	Direct sow	March 23 – April 11	3 wk before
🥬 Collards	Direct sow	March 23 – April 11	3 wk before
🥬 Collards	Set out	March 23 – April 11	3 wk before
🥒 Cucumbers	Start indoors	March 23 – April 11	3 wk before
🧅 Green Onions	Set out	March 23 – April 11	3 wk before
🥬 Kale	Direct sow	March 23 – April 11	3 wk before
🥬 Kale	Set out	March 23 – April 11	3 wk before
🥬 Kohlrabi	Direct sow	March 23 – April 11	3 wk before
🥬 Kohlrabi	Set out	March 23 – April 11	3 wk before
🥬 Leaf Lettuce	Direct sow	March 23 – April 11	3 wk before
🎃 Pumpkins	Start indoors	March 23 – April 11	3 wk before
🎃 Summer Squash	Start indoors	March 23 – April 11	3 wk before
🎃 Winter Squash	Start indoors	March 23 – April 11	3 wk before
🥒 Zucchini	Start indoors	March 23 – April 11	3 wk before
🥬 Bok Choy	Direct sow	March 30 – April 18	2 wk before
🥬 Bok Choy	Set out	March 30 – April 18	2 wk before
🥦 Broccoli	Set out	March 30 – April 18	2 wk before
🌿 Cilantro	Direct sow	March 30 – April 18	2 wk before
🥬 Leaf Lettuce	Set out	March 30 – April 18	2 wk before
🥬 Swiss Chard	Direct sow	March 30 – April 18	2 wk before
🥬 Swiss Chard	Set out	March 30 – April 18	2 wk before
🌿 Dill	Direct sow	April 6 – April 25	1 wk before
🫘 Bush Beans	Direct sow	April 20 – May 9	1 wk after
🥒 Cucumbers	Set out	April 20 – May 9	1 wk after
🎃 Pumpkins	Direct sow	April 20 – May 9	1 wk after
🎃 Pumpkins	Set out	April 20 – May 9	1 wk after
🎃 Summer Squash	Direct sow	April 20 – May 9	1 wk after
🎃 Summer Squash	Set out	April 20 – May 9	1 wk after
🌽 Sweet Corn	Direct sow	April 20 – May 9	1 wk after
🍅 Tomatoes	Set out	April 20 – May 9	1 wk after
🎃 Winter Squash	Direct sow	April 20 – May 9	1 wk after
🎃 Winter Squash	Set out	April 20 – May 9	1 wk after
🥒 Zucchini	Direct sow	April 20 – May 9	1 wk after
🥒 Zucchini	Set out	April 20 – May 9	1 wk after
🥒 Cucumbers	Direct sow	April 27 – May 16	2 wk after
🌶️ Okra	Direct sow	April 27 – May 16	2 wk after
🌶️ Okra	Set out	April 27 – May 16	2 wk after
🌶️ Peppers	Set out	April 27 – May 16	2 wk after
🫘 Southern Peas	Direct sow	April 27 – May 16	2 wk after
🍠 Sweet Potato	Set out	April 27 – May 16	2 wk after

Offsets are published guidance; the dates they land on are computed from measured NOAA normals. The seed-starting tool does this for your own ZIP code and counts the days.

What survives the winter changes across Carroll County

Zone 5a carries 48 of 74 perennial edibles; zone 5a carries 48.

Hardiness ranges are a judgement, published by growers rather than measured; the zone they are compared against is measured. On a warm-end verdict, check with your local extension service — a coastal zone 8 and an inland zone 8 are not the same summer.

Cautious — shortens the seasonMedian across stationsOptimistic

Last spring freeze: Plan to May 18 to be careful. Median April 13 – May 2 across 4 stations; April 1 is the optimistic end.
First fall freeze: Plan to September 23 to be careful. Median October 7 – October 26 across 4 stations; November 7 is the optimistic end.

NOAA publishes these as probabilities, not averages — the middle figure is a median, so half of years fall either side of it. The cautious end is the 10% tail: in roughly nine years in ten the freeze falls on the safe side of it.

The 4 stations behind these numbers

All 4 NOAA stations whose normals this page quotes, spanning about 44 km north to south. Every one is named with its identifier in the station list below — this page does not single one out, because no one station speaks for a whole county.

A relative sketch, not a map with a projection: longitude is adjusted for latitude so the shape is not stretched, and there is no basemap. For the one station nearest a specific address, with its real distance, use the ZIP lookup above.

These are the stations this county's ZIP codes actually cite as nearest — not a claim that each one sits inside its boundary, since a rural ZIP legitimately reaches over it. Every figure above comes from them, and each is named so you can check it.

Station	NOAA ID	Last spring freeze	First fall freeze	Season
Freeport Waste Wtp, IL	USC00113262	April 26	October 13	169 days
Fulton L&D #13, IL	USC00113290	April 13	October 26	195 days
Mt Carroll, IL	USC00115901	May 2	October 7	154 days
Polo 5Nw, IL	USC00116897	April 29	October 7	161 days

These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.

Your own ZIP

Work out your own dates

This page describes a whole county. Every tool below answers for one ZIP code, which is the grain the underlying data is published at.

Other places to compare

Carroll County sits in Illinois. That page carries the whole state's zone spread, its metro areas, and every other county in it with a page here.

More of Illinois

Counties with the same zones — 5a–5b

Matched on the exact zone set, not a dominant zone, so the winter answer on these pages really is the same one as here.

Gear

If you want to act on this

Each link opens an Amazon search rather than a product we picked. We have not tested these and do not rank them — the search is the honest version, and you choose.

Trunk wrapZone 5a is cold enough that winter sun on a young trunk does more damage than the cold does.
Row cover and frost clothThe season here closes at the first fall freeze dated above — a cover buys back some of those days at the end.
MulchFor the perennials nearest their cold limit in zone 5a, where an insulated crown is what decides whether they come back.

As an Amazon Associate we earn from qualifying purchases. That costs you nothing extra, and it buys no influence over anything on this site: the dates come from NOAA normals and the zones from the USDA, and no product affects either.

Sources

Where these numbers come from

Hardiness zones are the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. Freeze dates and growing-season lengths are NOAA 1991–2020 Climate Normals, taken per station and cited above by name and NOAA ID.

County boundaries come from the Census ZCTA-to-county relation, which is what places each ZIP code — and which treats parishes, boroughs and census areas as county equivalents. No station is chosen to represent this county: every range above is taken across all of them and the count is stated, because picking one would be a judgement dressed as a measurement.