Frost Line Depth in Stephenson County, IL: Rockford Requires 42 in

No official local value

No official frost line depth is published for Stephenson County.

Nearby official codes require 42 in (1 verified code).

Source and how we checked

We searched this place’s own code and website and found no published frost line depth.

Climate: 148 nights a year at or below 32 °F (NOAA 1991–2020, Freeport Waste Wtp, 4.8 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

42 in1 verified code within 31 mi
148nights a year at or below 32 °F
90%of nearby soil rated “high” for frost action (USDA)

Does Stephenson County have an official frost line depth?

No adopted frost line depth found for Stephenson County in its official documents (checked Oct 2026). The nearest official values, from codes we verified, are 42 in. Use the deepest of them until the building department confirms Stephenson County’s own number.

What frost line depth does Stephenson County use for footings under Table R301.2(1)? Is it 42 in, like Rockford?

Call 811 (JULIE) at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Stephenson County building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 42 in (the deepest nearby value) unless the building department tells you otherwise.
Book the footing inspection before you pour concrete.

How deep do footings, decks and water lines need to be in Stephenson County?

Drawn with the deepest nearby official value (42 in). Confirm Stephenson County’s own depth before you dig.

House or garage footing Deck footing Water service line Fence post

House or garage footing in Stephenson County: dig at least 42 in (107 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Using the nearby official value of 42 in until Stephenson County confirms its own
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 Stephenson County?

Average lows are at or below freezing from Nov to Mar. 148 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 11.3 °F.

NOAA 1991–2020 climate normals, Freeport Waste Wtp station, 4.8 mi away, elevation 750 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	11.3	14.8	25.8	36.4	48.4	58.6	62.3	59.9	51	39.3	28.2	17.9
High	27.9	32.6	44.9	58.2	69.9	79.3	82.4	80.7	74.3	61.5	46	33.3

Stephenson County has more freezing nights than 69 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 Stephenson County use?

One official code near Stephenson County is verified.

Official frost line depths near Stephenson County
Place	Verified frost line	Distance
Rockford	42 in	31 mi away

How likely is the soil in Stephenson County to heave?

High 90%

USDA rates the sampled soil around Stephenson County as 10% moderate, 90% high for frost action (main soils: Dubuque, Fayette, Virgil).

USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.

Stephenson County at a glance

Frost line depth: No official local value
Population (2023 est.): 43,105
Mean annual temperature: 47.7 °F
ZIP codes (19): 61007 · 61013 · 61018 · 61019 · 61027 · 61032 · 61039 · 61044 · 61047 · 61048 · 61050 · 61060 · 61062 · 61063 · 61067 · 61070 · 61078 · 61087 · 61089