Frost Line Depth in Macoupin County, IL: Decatur Requires 36 in

No official local value

No official frost line depth is published for Macoupin County.

Nearby official codes require 36 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: 110 nights a year at or below 32 °F (NOAA 1991–2020, Carlinville, 3.4 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

36 in1 verified code within 67 mi
110nights a year at or below 32 °F
66%of nearby soil rated “high” for frost action (USDA)

Does Macoupin County have an official frost line depth?

No adopted frost line depth found for Macoupin County in its official documents (checked Oct 2026). The nearest official values, from codes we verified, are 36 in. Use the deepest of them until the building department confirms Macoupin County’s own number.

What frost line depth does Macoupin County use for footings under Table R301.2(1)? Is it 36 in, like Decatur?

Call 811 (JULIE) at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Macoupin County building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 36 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 Macoupin County?

Drawn with the deepest nearby official value (36 in). Confirm Macoupin County’s own depth before you dig.

House or garage footing Deck footing Water service line Fence post

House or garage footing in Macoupin County: dig at least 36 in (91 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Using the nearby official value of 36 in until Macoupin County confirms its own
Project	Depth	Rule
House or garage footing	36 in	Below the frost line and at least 12 in deep (IRC R403.1.4)
Deck footing (attached)	36 in	Below the frost line and at least 12 in deep (IRC R507.3)
Water service line	42 in	6 in below the frost line and at least 12 in deep (IRC P2603.5)
Fence post bottom	36 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 Macoupin County?

Average lows are at or below freezing from Dec to Feb. 110 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 19.2 °F.

NOAA 1991–2020 climate normals, Carlinville station, 3.4 mi away, elevation 621 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	19.2	23	32.2	42.9	53.5	62.6	66	63.6	55.1	43.9	33.2	24.6
High	36.1	41.3	52.1	65.1	74.1	82.9	86.2	85	79.2	67	52.9	40.9

Macoupin County has fewer freezing nights than 57 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 Macoupin County use?

One official code near Macoupin County is verified.

Official frost line depths near Macoupin County
Place	Verified frost line	Distance
Decatur	36 in	67 mi away

How likely is the soil in Macoupin County to heave?

Moderate 34%High 66%

USDA rates the sampled soil around Macoupin County as 34% moderate, 66% high for frost action (main soils: Hickory, Virden, Velma).

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

Macoupin County at a glance

Frost line depth: No official local value
Population (2023 est.): 44,018
Mean annual temperature: 53.4 °F
ZIP codes (28): 62002 · 62009 · 62012 · 62014 · 62021 · 62023 · 62033 · 62044 · 62056 · 62063 · 62069 · 62074 · 62079 · 62085 · 62088 · 62093 · 62560 · 62572 · 62626 · 62630 · 62638 · 62640 · 62649 · 62667 · 62672 · 62674 · 62685 · 62690