Reading the wall
Not every crack is structural, and not every structural crack is urgent. The pattern, direction and width change over time are what tell you which one you have.
Fine vertical or slightly diagonal cracks in a poured concrete wall, often appearing within the first year or two after the pour, are typically shrinkage. Concrete loses volume as it cures and cracks where it is restrained, commonly at the corners of window and beam pockets where the section is reduced. These leak but they are not moving. Injection with epoxy or polyurethane seals them and, in the case of epoxy, restores some of the wall's tensile continuity. These are the straightforward ones and they should be priced as small jobs, not as structural work.
Horizontal cracking partway up a block wall is a different animal. It means lateral soil pressure has exceeded what the wall can resist, and it is common here because saturated clay backfill pushes hard, especially when frost drives into the top of the backfill zone and adds ice pressure to the soil load. Stair-step cracking through the mortar joints near a corner, cracks noticeably wider at the top than the bottom, or a wall that has visibly bowed inward all point at soil load or differential settlement rather than curing shrinkage. Sight down the wall from one end with your eye close to the surface. Bowing that is invisible standing back is obvious from that angle.
Sealing a moving crack is a temporary result. Where the wall is taking lateral load, the fix is reinforcement combined with relieving the water pressure outside. Where the crack is from settlement, the footing needs support before anything gets patched. The order matters: stabilize, then seal. A contractor who proposes injection on a wall that is visibly bowed is treating a symptom, and the crack will reopen. This is the single most useful question to ask about any crack quote: what is the mechanism, and does this repair address it or just close it.
Epoxy injection is rigid, adheres strongly, and structurally re-knits a crack in poured concrete. It is used when the goal is restoring the wall's continuity and when the crack is dry and stable. Polyurethane is flexible and foams on contact with water, which makes it the choice for active leaks and for cracks that may still see minor seasonal movement. Neither works well in block walls, because a hollow block wall is a different structure and the crack usually follows mortar joints rather than a single plane. Injection is a poured-wall technique. If someone proposes injecting a block wall, ask what exactly they are filling.
For a bowed wall the reinforcement options step up in capacity. Carbon fiber straps adhered to the interior face resist further inward movement and are low profile enough to finish over, but they hold the wall where it is rather than bringing it back, and they are generally suited to modest deflection. Steel I-beams braced against the floor joists handle greater loads and can sometimes achieve some straightening over time. Wall anchors, which tie the wall back to plates buried in the yard, can pull a wall back toward plumb but require enough open ground outside to install. Which is appropriate depends on how far the wall has moved and what access exists, and a straight answer to that is a reasonable thing to expect.
If you are not facing an urgent condition, measuring beats guessing. Mark the ends of the crack with a pencil line and the date, and record the width at a marked point with a feeler gauge, or fit an inexpensive crack monitor across it. Read it monthly for six months, ideally through a spring. A crack that has not changed through a wet season is telling you something important, and it may move a five-figure recommendation down to a small sealing job. A crack that has widened measurably in that window has also told you something, and you will approach the quote differently.
The top of the backfill against your basement wall is the part that freezes. Saturated silty clay in that zone expands as it freezes and adds pressure to the wall on top of the ordinary soil load, which is why bowing and horizontal cracking often visibly progress over a winter rather than through summer. This is also why footings are required to bear below the local frost line, and why the shallow footings under porches, stoops and unheated additions are so often the first things to move. Reducing the water in that backfill zone through grading and discharge control reduces the winter load directly.
Read this part carefully. Many crack repair warranties cover the seal against water intrusion at that specific crack, and explicitly exclude new cracks, structural movement, and hydrostatic pressure elsewhere in the wall. That may be entirely reasonable for a shrinkage crack injection. It is far less useful on a wall that is under load. Ask whether the warranty is transferable to a future owner, whether it survives a change of contractor ownership, and what specifically voids it. Get the answer in the contract rather than in conversation.
Knowing which you have changes how the wall should be read. A poured concrete wall is monolithic, so it cracks through the section, usually vertically, and injection is a meaningful repair because you are re-knitting a single plane. A concrete block wall is an assembly of units and mortar joints, so it fails along those joints in stair-step or horizontal patterns, and there is no single plane to inject. Block walls are also considerably weaker in bending, which is why horizontal cracking from lateral soil pressure is far more common in block than in poured construction. Older Champaign and Urbana basements are frequently block. Newer construction is generally poured. The repair vocabulary is not interchangeable between them.
Cracks in a basement floor slab worry homeowners more than they usually should. A basement slab is typically a non-structural pour sitting on the ground inside the foundation walls, carrying nothing but itself, and it commonly cracks from shrinkage as it cured. Those are hairline, meandering, and level on both sides. The ones worth attention are cracks where one side sits higher than the other, cracks that have opened wide enough to see into, and cracks that actively pass water. Displacement in a floor slab means the ground beneath it has moved differentially, which is a soil question rather than a concrete question, and it should be looked at alongside the walls rather than patched in isolation.
Before you hire anyone in Illinois: there is no statewide general contractor license in this state. Contractor registration is handled by individual municipalities, and the City of Champaign requires contractors to be registered with the city to pull a permit. Ask who is pulling the permit, ask for written proof of liability coverage and workers' compensation, and get the scope in writing.
Photograph the crack with something for scale and note the date, then get in touch. Call (217) 882-0544 or send the form, and an independent foundation contractor working in Champaign County will follow up with you directly.
Call and describe it. It costs nothing to find out whether you are looking at a maintenance item or a structural one.