Illinois Ground Snow Load: Who Sets It

Illinois sets no ground snow load at state level, so every figure comes from a county or city building department. The body to ask is your city, village, or county code official. 19 states work this way, which is why a search for one Illinois figure comes back with several different answers from several different pages, all of them correct for the place they were written for. Illinois publishes ground snow loads through your city, village, or county code official, and the jurisdictions reached for this had put none into a public document at the time they were read.

Your city, village, or county code official: the state board that oversees construction codes publishes no snow load figures and says the code official where the work is has the answer. In its own words: “The best and most accurate answers to building code questions must be answered by your city, village, or county code official.”

Capital Development Board adopts Local codes and amendments; where a jurisdiction has adopted none, the International Residential Code for residential work and the International Building Code for commercial work, as required by statute (IRC current edition (1/1/24 excluding IV and VII); IBC current edition or most recent preceeding edition (1/1/25 Incl. App G., Excl. Ch 11, 13, 29)). Illinois adopted it as written. The adopting rule reads: “Starting 1/1/25 local codes must regulate the structural design in a manner that is at least as stringent as the IRC.”

A ground snow load is a weight per unit area and not a depth, and the two are joined only by the density of the snow on the day, which is why the published documents give the load and leave the depth out. Wet spring snow and dry January snow of the same depth are different weights on the same roof. Your city, village, or county code official works in loads for that reason, and so does every figure set out below.

A Illinois figure for an address the documents below do not cover comes from your city, village, or county code official. The document behind it is Building Codes and Regulations, published by Capital Development Board, read on September 23, 2026. It establishes the point this way: “Until then, units of local government such as cities and counties can adopt codes of their choice. The best and most accurate answers to building code questions must be answered by your city, village, or county code official.”

14 of 50: Connecticut, Indiana, Maryland, Massachusetts, Michigan, Minnesota, Montana, New Hampshire, New Jersey, North Carolina, Rhode Island, Utah, Vermont, Wisconsin. The other 36 split into 17 that adopt the national code without a snow amendment and 19 that leave every figure to a county or city building department. That is the single most useful fact about this subject and no one state's own website carries it.