Frost Line Depth in Rock Island County, Illinois
- Rock Island County’s adopted code
- Checked Oct 2026
- Sources
Verified
42in
107 cm · 3 ft 6 in
Set in the building code Rock Island County has adopted.
Source and how we checked
Document: rockislandcountyil.gov
Climate: 129 nights a year at or below 32 °F (NOAA 1991–2020, Moline Quad City International Airport, 2.5 mi).
Checked Oct 2026. Report a correction
How deep is the frost line in Rock Island County?
Rock Island County's building authority sets the frost line depth at 42 in (107 cm). Footings, piers and other permanent supports must reach at least this depth (IRC R403.1.4.1).
Who sets the frost line depth in Rock Island County?
Illinois leaves the frost line depth to each city or county, and Rock Island County fills it in when it adopts the residential code. The value above comes from Rock Island County’s own document on rockislandcountyil.gov. See how Illinois sets frost line depth.
How deep do footings, decks and water lines need to be in Rock Island County?
House or garage footing in Rock Island 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 Rock Island County?
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Average lows are at or below freezing from Nov to Mar. 129 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 14.8 °F.
NOAA 1991–2020 climate normals, Moline Quad City International Airport station, 2.5 mi away, elevation 592 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 14.8 | 18.8 | 29.6 | 39.9 | 51.1 | 61 | 64.9 | 62.7 | 54.2 | 42.6 | 30.9 | 20.8 |
| High | 31.8 | 36.6 | 49.9 | 63 | 73.9 | 83.1 | 86.1 | 84.1 | 77.9 | 64.8 | 49.8 | 37 |
Rock Island County has more freezing nights than 41 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 Rock Island County use?
One official code near Rock Island County is verified.
| Place | Verified frost line | Distance |
|---|---|---|
| Peoria County | 42 in | 63 mi away |
How likely is the soil in Rock Island County to heave?
USDA rates the sampled soil around Rock Island County as 5% low, 37% moderate, 58% high for frost action (main soils: Fayette, Waukee, Raddle).
USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.
How do you confirm the frost line before you dig in Rock Island County?
Rock Island County at a glance
- Frost line depth
- 42 in
- Population (2023 est.)
- 141,236
- Mean annual temperature
- 51.2 °F
- ZIP codes (21)
- 61201 · 61232 · 61236 · 61237 · 61239 · 61240 · 61242 · 61244 · 61256 · 61257 · 61259 · 61264 · 61265 · 61272 · 61273 · 61275 · 61278 · 61279 · 61281 · 61282 · 61284