Composite Deck costs $42.02 to $89.28 per sq ft in Illinois in 2026. For a 400 sq ft project, that puts the installed total at $16,806 – $35,714, with most projects landing near $26,260. Illinois is about 5% above the national average.
Why Illinois prices differ from the national average
Roughly 42% of the installed cost of composite deck is labor, and labor is the part of the bill that actually moves between states. Illinois construction wages average $41.41 per hour against a national figure near $36.97 — a wage index of 1.12×.
Materials behave differently. Framing lumber, decking boards, fasteners, and railing are priced on national commodity and manufacturer markets, so material costs barely move from one state to the next. That is why we apply the wage index only to the labor share and hold materials at national prices. Doing that puts Illinois at $42.02 to $89.28 per sq ft, against a national baseline of $40.00 to $85.00.
Two other forces sit on top of that. Metro areas inside Illinois price above the statewide figure because of wages, permitting, and site access. And the state’s deep frost line adds excavation and below-grade volume that southern states never pay for.
Composite Deck cost by project size in Illinois
These figures apply the Illinois rate to common project sizes. They cover a standard specification with normal site access.
| Project size | Illinois cost range | Typical |
|---|---|---|
| 10×10 (100 sq ft) | $4,202 – $8,928 | $6,565 |
| 12×12 (144 sq ft) | $6,050 – $12,857 | $9,454 |
| 12×16 (192 sq ft) | $8,067 – $17,143 | $12,605 |
| 12×20 (240 sq ft) | $10,084 – $21,428 | $15,756 |
| 16×20 (320 sq ft) | $13,445 – $28,571 | $21,008 |
| 20×20 (400 sq ft) | $16,806 – $35,714 | $26,260 |
Where the money actually goes
For a 400 sq ft project in Illinois at roughly $26,260, a typical bill splits like this:
| Line item | Share | Cost |
|---|---|---|
| Labor | 42% | $11,029 |
| Materials | 44% | $11,423 |
| Site prep & equipment | 9% | $2,285 |
| Overhead, disposal & finishing | 6% | $1,523 |
The labor share is why identical projects diverge so sharply between states. It is also why a bid that comes in far below these numbers usually means a thinner specification or a crew cutting site prep, not a genuine bargain.
Composite Deck cost by city in Illinois
Statewide averages hide a lot. Chicago, Naperville, Springfield all price above the Illinois average, while rural counties run below it:
| Area | Cost per sq ft | A 400 sq ft project | vs state |
|---|---|---|---|
| Chicago | $49.58 – $105.36 | $30,987 | +18% |
| Naperville | $47.06 – $100.00 | $29,411 | +12% |
| Springfield | $42.02 – $89.28 | $26,260 | +0% |
| Rural Illinois | $39.07 – $83.03 | $24,422 | −7% |
What is included in a Illinois quote — and what is not
A complete quote for this work should list dimensions, specification and grade, site preparation, materials, labor, cleanup, and disposal. Those are the items already reflected in the ranges above.
Costs that usually sit outside the headline number: permits (around $600 in Illinois), demolition or removal of existing work, unusual site access, drainage or grading corrections, and any upgrade to the standard specification. When two bids differ by thousands, the gap is nearly always one of these, not the labor rate.
Frost depth and code requirements in Illinois
Permits in Illinois
A residential permit for work of this type and value in Illinois typically runs around $600, though the figure varies by municipality and often scales with declared project value. Permit cost is rarely folded into a contractor’s per-sq ft quote, so add it separately when comparing bids. Confirm requirements with your local building department before work begins — unpermitted work can surface later during a sale or insurance claim.
Best time of year to schedule in Illinois
Weather closes the working window in Illinois. Concrete and exterior work generally run from late spring through early autumn, and crews book out well before then. Cold-weather work is possible with blankets, heated enclosures, or accelerating admixtures, but those add cost. Booking in late winter for spring work usually secures better pricing than calling in June.
DIY versus hiring a contractor in Illinois
Materials account for roughly 58% of the installed price, so a 400 sq ft project carries about $15,231 in materials against an installed cost near $26,260. The gap is labor, equipment, and the risk of getting it wrong.
Because Illinois labor runs at 1.12× the national rate, the DIY saving here is larger than in most states, which makes self-performing more tempting. Weigh it against tool rental, waste disposal, permit responsibility, and the fact that remedial work almost always costs more than doing it right the first time.
How Illinois compares with nearby states
Illinois sits in the Midwest region. Here is how neighbouring states price the same specification:
| State | Cost per sq ft | vs Illinois |
|---|---|---|
| South Dakota | $37.48 – $79.65 | Lower than Illinois |
| Kansas | $38.82 – $82.50 | Lower than Illinois |
| Nebraska | $38.99 – $82.86 | Lower than Illinois |
| Iowa | $39.16 – $83.22 | Lower than Illinois |
| Missouri | $39.16 – $83.22 | Lower than Illinois |
| Indiana | $39.33 – $83.57 | Lower than Illinois |
Getting an accurate number for your project
Everything above is a planning range. Enter your real dimensions and specification to get a figure with Illinois rates already applied:
Open the composite deck calculator →Then get three written, itemised quotes. Make sure each one specifies the same dimensions and the same grade of material — that is the only way a comparison means anything.
Frequently asked questions
How much does composite deck cost in Illinois?
In 2026, composite deck costs $42.02 to $89.28 per sq ft in Illinois. For a 400 sq ft project, the installed total typically lands between $16,806 and $35,714, with most projects near $26,260.
Is composite deck more expensive in Illinois than the national average?
Illinois is about 5% above the national average. The driver is a construction wage index of 1.12 times the national figure, applied to the roughly 42% of the project cost that is labor.
Which parts of Illinois are most expensive?
Chicago, Naperville, and Springfield price above the statewide average because of higher wages, stricter permitting, and tighter site access. Rural counties typically run around 7% below the state figure.
Do I need a permit in Illinois?
Most municipalities in Illinois require a permit for work of this type and value. Budget around $600 and confirm with your local building department before work starts, since requirements vary between cities and counties.
How deep is the frost line in Illinois?
The frost line in Illinois is roughly 42 inches. Footings and posts must extend below that depth to avoid frost heave, which adds excavation and material to the job.
When is the cheapest time to book this work in Illinois?
Weather closes the working window in Illinois. Concrete and exterior work generally run from late spring through early autumn, and crews book out well before then. Cold-weather work is possible with blankets, heated enclosures, or accelerating admixtures, but those add cost. Booking in late winter for spring work usually secures better pricing than calling in June.
How much of the cost is labor versus materials?
Labor is about 42% of the installed price and materials about 58%. That split is why state wage differences move the total so much, and why material price swings move it less than people expect.
Why do contractor quotes in Illinois vary so much?
Three things move a quote most: metro versus rural location, site access and preparation, and the specification itself. Two bids are only comparable when both list the same dimensions, the same grade of material, and the same scope of prep work.