Frost Line Depth in Knox County, Illinois
- 3 verified codes nearby
- Checked Oct 2026
No official local value
No official frost line depth is published for Knox County.
Nearby official codes require 40–42 in (3 verified codes).
Source and how we checked
We searched this place’s own code and website and found no published frost line depth.
Climate: 135 nights a year at or below 32 °F (NOAA 1991–2020, Knoxville, 4.4 mi).
Checked Oct 2026. Report a correction
Does Knox County have an official frost line depth?
No adopted frost line depth found for Knox County in its official documents (checked Oct 2026). The nearest official values, from codes we verified, are 40 to 42 in. Use the deepest of them until the building department confirms Knox County’s own number.
What frost line depth does Knox County use for footings under Table R301.2(1)? Is it 42 in, like Peoria County?
How deep do footings, decks and water lines need to be in Knox County?
Drawn with the deepest nearby official value (42 in). Confirm Knox County’s own depth before you dig.
House or garage footing in Knox County: dig at least 42 in (107 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).
| Project | Depth | Rule |
|---|---|---|
| House or garage footing | 42 in | Below the frost line and at least 12 in deep (IRC R403.1.4) |
| Deck footing (attached) | 42 in | Below the frost line and at least 12 in deep (IRC R507.3) |
| Water service line | 48 in | 6 in below the frost line and at least 12 in deep (IRC P2603.5) |
| Fence post bottom | 42 in | No code rule; common practice is below the frost line |
Work out posts, concrete and footing sizes with the fence post depth calculator or the deck footing calculator.
How cold does it get in Knox County?
- J
- F
- M
- A
- M
- J
- J
- A
- S
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- N
- D
Average lows are at or below freezing from Nov to Mar. 135 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 14.3 °F.
NOAA 1991–2020 climate normals, Knoxville station, 4.4 mi away, elevation 728 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 14.3 | 18.1 | 28.5 | 39.4 | 50.8 | 60.7 | 64.7 | 62.6 | 54.4 | 41.8 | 30.7 | 20.5 |
| High | 31.6 | 36.1 | 48.8 | 61.5 | 72 | 81.2 | 83.6 | 82 | 76.3 | 63.8 | 49.3 | 36.4 |
Knox County has more freezing nights than 52 of the 71 other Illinois places we track. The Illinois median is 127. Coldest: Hoffman Estates; mildest: Madison County.
What frost line depth do towns near Knox County use?
3 official codes near Knox County are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Peoria County | 42 in | 25 mi away |
| Bloomington | 40 in | 72 mi away |
| LaSalle County | 42 in | 75 mi away |
How likely is the soil in Knox County to heave?
USDA rates the sampled soil around Knox County as 40% moderate, 60% high for frost action (main soils: Hickory, Ipava, Rozetta).
USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.
Knox County at a glance
- Frost line depth
- No official local value
- Population (2023 est.)
- 48,411
- Mean annual temperature
- 50.4 °F
- ZIP codes (23)
- 61401 · 61402 · 61410 · 61414 · 61428 · 61430 · 61434 · 61436 · 61439 · 61448 · 61449 · 61458 · 61467 · 61472 · 61474 · 61485 · 61488 · 61489 · 61490 · 61529 · 61531 · 61544 · 61572