In Illinois, a non-conforming use is:

A non-conforming use is not illegal — it is a legally protected status specifically because the use predates the zoning restriction that would otherwise prohibit it. Calling it 'always illegal' confuses a non-conforming use with an illegal use, which is one that was never authorized by any applicable zoning ordinance.

A use requiring a special permit is called a 'special use' or 'conditional use,' which is a separate zoning concept entirely distinct from a non-conforming use. A special use requires affirmative approval from the zoning board before it can operate, whereas a non-conforming use already exists and continues by right without needing new government approval.

Non-conforming uses generally cannot be expanded freely; Illinois municipalities typically prohibit enlargement, extension, or intensification of a non-conforming use because expansion would increase the degree of non-conformity and undermine the municipality's long-term planning goals. Allowing free expansion would effectively reward non-conformity and defeat the purpose of zoning amendments.