If you need a handful of pallets for a project, there are plenty in Chicago. They sit where industry is, and every one of them belongs to someone.
Where they pile up
Pallets build up behind warehouses, plants and big stores. In the city, the largest concentrations of industrial land are the City's industrial corridors; the biggest by area in the City's dataset are Calumet (4,197 acres), Stockyards (1,498 acres), Little Village (1,252 acres), Stevenson (1,245 acres), Pilsen (1,070 acres).
Ask first
A stack behind a building is somebody's property, even when it looks like trash. Ask at the dock or the front desk. Small businesses with a few broken pallets are often glad to see them go; big warehouses usually have a buyer already and may say no.
Leave the painted ones
Blue, red and other painted or branded pallets are pooled: rented, not owned, by the business they're sitting behind. Don't take them. See pooled pallets in Illinois.
When to buy instead
If you need the same size and grade every week, or more than a pickup truck holds, free piles won't keep up. Use the find pallets form and a seller who covers your ZIP will reply.